Low-hydrogen photovoltaic cell

ABSTRACT

A low-hydrogen photovoltaic cell is disclosed. The photovoltaic cell may contain less than 5% hydrogen. In one aspect, the photovoltaic cell may contain substantially no hydrogen, that is, the photovoltaic cell may be substantially hydrogen free. The photovoltaic cell includes a substrate and an absorber deposited on to the substrate. The absorber may typically include elements from group 11, group 12, and group 13 of the Periodic Table, for example, copper, indium, and gallium. The absorber may be treated with selenium and/or sulfur to produce a CIGS or CIGSS-type photovoltaic cell. The low-hydrogen photovoltaic cell may fabricated by a method and apparatus adapted to control metalloid vapor delivery, for example, in a low-hydrogen or hydrogen free atmosphere.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of co-pending applicationSer. No. 11/282,934 filed on Nov. 18, 2005 [attorney docket no.2606.002], the disclosure of which is incorporated by reference hereinin its entirety.

TECHNICAL FIELD OF THE INVENTION

The present invention relates to methods and apparatus for exposing amaterial or work piece to a vaporous element. Specifically, the presentinvention provides methods and apparatus for treating a photovoltaicprecursor with a vaporous element, for example, selenium or sulfur, toproduce thin film CIGS or CIGSS solar cells.

BACKGROUND OF THE INVENTION

The limited availability of and environmental concerns about fossilfuels make them increasingly less attractive as a means to produceelectricity. As a result of this trend, alternative energy sources,particularly solar energy, are becoming more popular. While solar energyis a reliable and dependable energy source, the costs associated withsolar energy production have traditionally limited its availability anddesirability as a substitute for fossil fuels. However, recenttechnological advances in solar cell manufacturing show promise to lowerthe cost of solar energy.

Solar energy proponents and researchers state that higher solar cellefficiency and lower production costs are two ways to reduce the overallcost of solar energy. In particular, solar cells with absorber materialscomprised of copper, indium, gallium, and selenium and/or sulfur[hereinafter Cu(In,Ga)(S,Se)₂ or CIGS] show promise in higherefficiency, lower production costs, and long operational lifetimes.These absorber materials are the result of innovative thin-filmmanufacturing technologies that further reduce manufacturing costs bylowering raw material costs and increasing throughput and efficiencies.

As is commonly practiced in the art, these CIGS cells are manufacturedin either a one-stage thermal co-evaporation process or a two-stageprocess. The single stage thermal co-evaporation process consists ofdepositing all of the CIGS elements onto a substrate and simultaneouslyheating that substrate temperature to approximately 450° C. to 600° C.to allow the constituent materials to form a crystal matrix in theabsorber.

Although the one-step co-evaporation process is of interest to CIGSmanufacturing, the two-step process may be more manufacturable and posesunique challenges of its own. In the first step of the two-step process,a material is deposited upon a substrate. The material deposited on thesubstrate is referred to as the “precursor.” The precursor may compriseone or more of copper (Cu), indium (In), gallium (Ga), and/or selenium(Se) and/or sulfur (Se). Usually the precursor is a mixture of copper,indium, and gallium. In the second step of the two-stage process of CIGSmanufacturing, selenium or sulfur is introduced into the precursor by aprocess known in the art as “selenization.” Selenization typicallyincludes heating the precursor in a selenium-rich (or sulfur-rich)environment until the elements react to make a crystal matrix to formthe chalcopyrite CIGS material that becomes known as the “absorber.”Common sources of selenium or sulfur in CIGS manufacturing includevaporizing powdered selenium or sulfur, hydrogen selenide, hydrogensulfide, or organic compounds of selenium or sulfur with low evaporationpoints. This process has been accepted by researchers in solar cellmanufacturing methods as an acceptable means of introducing selenium orsulfur into the absorber material; however, this technique also posessubstantial risks and costs. Further, as some researchers may blendcertain elements of the one-stage and two-stage process, thesechallenges may apply to the one-stage process as well.

Selenization is usually practiced by two methods. In one prior artmethod, selenium pellets are placed in a receptacle, or “boat,” in achamber and then the selenium and precursor are heated to release aselenium-containing vapor which interacts with the precursor. In theother prior art method the treatment chamber is filled with selenium orsulfur vapor or with hydrogen selenide (H₂Se) or hydrogen sulfide (H₂S)gas. Sometimes a process will involve placing hydrogen (H₂) gas in thetreatment chamber while heating the Se or S pellets to form H₂Se or H₂Sin situ. These two methods are essentially the only methods ofselenizing photovoltaic precursors.

Due to the nature of the chemical reactions, an excess amount of Se oran over-pressure of Se is desirable during the selenization process. Anexcess of Se is typically necessary since the reaction of the Cu, In,Ga, and Se tends to “push” at least some of the Se out of the precursorat elevated temperature. Therefore, it is believed that, without excessSe present, any deposited Se will tend to evaporate out of the precursormatrix and not bind to the matrix as desired. Aspects of the presentinvention overcome this barrier by providing sufficient Se to minimizethe escape of Se from, for example, the Cu—In—Ga matrix.

With regards to thermal co-evaporation, some prior art co-evaporationprocesses “hint” that selenization may be used to “fix” a film thatmight not be quite right stoichiometrically. That is, afterco-evaporation, the precursor may lack sufficient Se whereby further Seaddition is required to provide the desired stoichiometric quantity ofSe. This further selenization is typically practiced by one of themethods discussed above.

Current CIGS manufacturing techniques also have serious health andenvironmental implications. As discussed below, various manufacturingtechniques have been used to introduce selenium or sulfur into theabsorber material matrix with varying success. Although somemanufacturing methods are more reliable, the health or environmentalconcerns, especially in large-scale production volumes, make themundesirable for long-term use. More specifically, the use of the highlytoxic hydrogen selenide and its derivatives is expensive because ofneeded safety precautions. While CIGS solar cells show great promise insolar cell manufacturing to reduce raw material costs, safe, reliable,and repeatable methods to introduce selenium or sulfur into the matrixare needed.

Prior art also suggests that CIGS solar cells produced by selenizationprocesses have performance problems that may be unique to themanufacturing method. Recent studies by P. K. Johnson and A. E. Delahoyshowed that solar cells produced by selenization had higher defectdensities, “light-inhibited” degradation of cell efficiency of up to97%, and a 13% reduction in Voc×FF over a 30 to 45 day period. Incontrast, solar cells produced by thermal co-evaporation showed lowerdefect densities, lower cell efficiency reduction, and less than a 2%reduction in Voc×FF over a 30 to 45 day period. The key distinguishingfeature of most selenization processes and thermal co-evaporation isthat selenization usually uses a hydrogen-containing species, H₂Se.Although some of the decreased product performance of selenized solarcells is due to encapsulation method of the module and migration ofsodium from the soda lime substrate into the absorber matrix, a goodportion of the discrepancies in cell performance have to do withmanufacturing method. While the enhanced product performance factorsmake thermal co-evaporation more desirable, selenization process methodsare more suited to manufacturing high efficiency cells on large areasubstrates.

Additionally, H₂Se is incompatible with stainless steel and other metalsthat have the potential to replace soda lime glass as a substratematerial. This distinction is increasingly important as solar cellmanufacturers look to lower manufacturing costs while increasing thenumber of form factors available for “finished” solar cell devices.Thus, in addition to the safety and environmental concerns, a solar cellmanufacturing method that comprises 1) the low hydrogen advantages ofthermal co-evaporation on long term cell performance, 2) themanufacturing capability high efficiency solar cells on large areasubstrates, and 3) compatibility with stainless steel and other metalsis also needed.

DESCRIPTION OF THE RELATED ART

Within the art of CIGS manufacturing, the selenization process is oftencompleted in a chamber. These chambers are either rectangular, square,or round and may or may not have shelves. An exemplary embodiment of atypical chamber is disclosed in U.S. Pat. No. 6,787,485 by Probst[herein “Probst”] and a typical selenization method is disclosed in U.S.Pat. No. 5,045,409 by Eberspacher, et al. [herein “Eberspacher”]. Inparticular, Probst discloses a “stack oven” with an adjustable gasatmosphere capable of operating in vacuum. Additionally, the Probstapparatus comprises heating elements and shelves that contain theprocess items in an arrangement that interleaves the process items andthe energy sources, with at least one energy source per process item.The heating sources are arranged in a quartz glass envelope, with aliquid or gas coolant flowing through the envelope. Probst focuses onthermal uniformity of the substrates, however, unlike aspects of thepresent invention, Probst does not disclose 1) a high utilization rateof selenium of at least 90%, 2) a solid source of the processing vapor,3) an enhanced means to control delivery of selenium or sulfur vapor, 4)a condenser/evaporator to deliver vapor from a solid source, 5) a vaportight inner chamber space, nor 6) an independent thermal control of thesubstrates, a condenser/evaporator, and the walls of the chamber.Aspects of the present invention may provide one or more of theseadvantages over Probst.

Eberspacher discloses a method to form a CIS or CIGS film without usingH₂Se, which is a highly toxic gas and is thus unsuitable for large scalemanufacturing because of safety concerns. In the disclosed method ofEberspacher, a mixture of copper and indium or copper, indium, andgallium are deposited on a substrate by sputtering. A selenium film isthen deposited by thermal evaporation. The substrate is then heated inthe presence of hydrogen, H₂Se, or H₂S to form the crystalline matrixfor the solar cell absorber material. While the inventor's aim was tototally eliminate the use of H₂Se, the inventor admits in thespecification that a low concentration of H₂Se is needed to improve cellperformance. Eberspacher further discloses a “conventional thermalevaporation method” which takes place in an oven with a gas inlet andoutlet, but, unlike aspects of the present invention, does notdisclose 1) a solid source of the processing vapor, 2) a highutilization rate of selenium of at least 90%, 3) a means to controldelivery of selenium or sulfur vapor, 4) a condenser/evaporator todeliver vapor from a solid source, 5) a vapor tight inner chamber space,nor 6) an independent thermal control of the substrates, acondenser/evaporator, and the walls of the chamber. Aspects of thepresent invention may provide one or more of these advantages overEberspacher.

U.S. Pat. Nos. 6,092,669 and 6,048,442 Kushiya, et al. [collectivelyherein “Kushiya”] discloses a method and apparatus for producing athin-film solar cell. Specifically, Kushiya discusses processing thesolar cells by heating them in an atmosphere of selenium or sulfur.According to Kushiya, the substrates are heated in an electric furnacewith an undisclosed reactive gas at a temperature not higher than 600°C. Unlike aspects of the present invention, Kushiya does not disclose 1)a solid source of the processing vapor, 2) a high utilization rate ofselenium of at least 90%, 3) a means to control delivery of selenium orsulfur vapor, 4) a condenser/evaporator to deliver vapor from a solidsource, 5) a vapor tight inner chamber space, nor 5) an independentthermal control of the substrates, a condenser/evaporator, and the wallsof the chamber. Aspects of the present invention may provide one or moreof these advantages over Kushiya.

U.S. Pat. No. 6,518,086 of Beck, et al. [herein “Beck”] discloses atwo-stage process to produce a CIGS or CIGSS film on a substrate forsemiconductor applications. While referencing the prior art, Beckdiscusses the exemplary inventions of the two best known methods ofselenization: (1) vapor deposition of the constituent elements followedby heating (see U.S. Pat. No. 5,141,564 issued to Chen, et al. (herein“Chen”)) and (2) a two-stage process wherein selenium or sulfur is addedto the absorber crystal matrix by heating copper indium alloys with H₂Seor Se vapor (see U.S. Pat. No. 4,798,660 issued to Ermer, et al. (herein“Ermer”) and U.S. Pat. No. 4,915,745 issued to Pollock, et al.) Beckdistinguishes the first CIGS process of the Chen species as undesirablefor industrial scale manufacturing because of high temperatures to formthe absorber matrix. Beck further distinguishes the second selenizationprocess of the Ermer species as undesirable because of the use of highlytoxic H₂Se, low selenium utilization, and poor adhesion to molybdenumcoated substrates.

Beck discloses depositing a precursor layer of copper, indium, gallium,selenium, or sulfur in some combination to a substrate. These substratesare then heated in either an inert atmosphere comprising argon, xenon,helium, or nitrogen or under a selenium or sulfur vapor. The seleniumvapor can come from evaporating selenium from a “boat” inside thechamber, H₂Se, or diethylselenide. Similar to recognized methods ofselenization, Beck selenizes its precursor by heating theselenium-containing boat and precursor in the treatment chamber toproduce the Se vapor and holds the boat and precursor at temperatureuntil selenization is complete. Contrary to aspect of the presentinvention, Beck does not disclose 1) a high utilization rate of seleniumof at least 90%, 2) a means to control delivery of selenium or sulfurvapor, 3) a condenser/evaporator to deliver vapor from a solid source,4) a vapor tight inner chamber space, nor 5) an independent thermalcontrol of the substrates, a condenser/evaporator, and the walls of thechamber. Aspects of the present invention may provide one or more ofthese advantages over Beck.

While the disclosed prior art is not exhaustive, it is representative ofwhat is known and practiced for selenization. In particular, in contrastwith aspects of the present invention, prior art vacuum chamberapparatuses and treatment methods do not disclose 1) an independentcontrol of substrate temperature, 2) a high utilization rate of seleniumof at least 90%, 3) high throughput capability with enhanced thermalmanagement, 4) controlled release and capture of selenium to the sameplace repeatedly, 5) independent control of the vapor pressure deliveryof sulfur or selenium, 6) vacuum compatible selenium delivery andtemperature control, 7) distinct temperature zones and valves to allowuse of traditional elastomer seals and vacuum gauges, and 8) futureprocess automation upgrade capability. Aspects of the present inventionprovide these other advantages and benefits not found in the prior art.

SUMMARY OF ASPECTS OF THE INVENTION

The present invention provides methods and apparatus for treatingmaterials with vaporous elements and compounds that enhances theversatility and adaptability of the treatment process. Though aspects ofthe invention may be utilized in the manufacture and processing ofphotovoltaic material, aspects of the invention are not limited toprocessing photovoltaic material, but can be applied to the treatment ofany material where the control and regulation of treatment temperatureimpacts the cost, quality, or performance of the product produced.

One aspect of the invention is a method for treating a work piece, forexample, a CIG photovoltaic precursor, with one or more vaporouselement. The method includes introducing the work piece and anelement-containing material to an enclosure; heating the work piece to afirst temperature; independent of the heating of the work piece, heatingthe element-containing material to a temperature sufficient tovolatilize the element and release an element-containing vapor into theenclosure; reacting at least some of the element-containing vapor withthe work piece; regulating the temperature of the element-containingmaterial at a temperature sufficient to condense at least some of theelement from the element-containing vapor on the element-containingmaterial; and cooling the work piece to provide an element-treated workpiece. In one aspect, the element comprises elemental sulfur or seleniumor combinations of sulfur, selenium, tellurium, indium, gallium, orsodium. In another aspect, cooling the element-containing material maycomprise cooling the element-containing material wherein substantiallyall of the unreacted element-containing vapor condenses on theelement-containing material.

Another aspect of the invention is an apparatus for treating a workpiece with a vaporous element, the apparatus including an enclosure;means for supporting the work piece in the enclosure; means for varyingthe temperature of the work piece; an element-containing material in theenclosure; means for varying the temperature of the element-containingmaterial to produce an element-containing vapor, the means for varyingthe temperature of the element-containing material being independent ofthe means for varying the temperature of the work piece; and means forexposing at least some of the work piece to the element-containingvapor. In one aspect, the enclosure comprises an inner enclosure, andwherein the apparatus further comprises an outer enclosure enclosing theinner enclosure.

Another aspect of the invention is a method for preparing a treatmentchamber for treating a work piece with a volatilizable element, themethod including introducing a solid element-containing material to thetreatment chamber, the treatment chamber comprising an internal cavity;heating the solid element-containing material to volatilize the elementand produce an element-containing vapor in the internal cavity;regulating the temperature of a surface exposed to the internal cavityto a temperature at which the element-containing vapor condenses; andcondensing at least some of the volatilized element from theelement-containing vapor onto the surface. In one aspect, the methodfurther includes regulating the temperature of the solidelement-containing material to a temperature below the volatilizationtemperature of the element, for example, whereby at least some of theelement from the element-containing vapor condenses onto the solidelement-containing material.

A still further aspect of the invention is a treatment chamber isolationapparatus, the treatment chamber having an opening, the isolationapparatus including a sealing assembly having a support structure; atleast one cover plate adapted to engage the treatment chamber opening; aplurality of rods having a first end adapted to engage the supportstructure and a second end adapted to engage the at least one coverplate; and means for compressing the sealing assembly against thetreatment chamber wherein the at least one cover plate engages thetreatment chamber opening to provide at least some isolation of thetreatment chamber. In one aspect, the first ends of the plurality ofrods are resiliently mounted to the support structure, for example, bymeans of springs and/or flexures.

Another aspect of the invention is a treatment chamber isolationapparatus, the treatment chamber having a cylindrical enclosure havingan open first end, a closed second end, and an internal flange mountedbetween the first end and the second end, the apparatus including asealing plate adapted to engage the internal flange; a support rodhaving a first end and a second end mounted to the sealing plate; aplate mounted to the second end of the support rod; and at least oneactuator adapted to displace the plate whereby the sealing plate engagesthe internal flange of the cylindrical enclosure and substantiallyisolates at least part of the cylindrical enclosure. In one aspect, thetreatment chamber isolation apparatus may further comprise a cylindricalextension mounted to the open first end of the cylindrical enclosure.

Another aspect of the invention is a material delivery device includinga cylindrical body having at least one outer surface; a volatilizablematerial applied to the at least one outer surface; means for varyingthe temperature of the at least one outer surface to regulate thevolatilization of the volatilizable material. In one aspect, the meansfor varying the temperature comprises a heat exchanger having a workingfluid passing through it.

Another aspect of the invention is a method of delivering a volatilematerial including providing a cylindrical body having at least oneouter surface; applying a volatilizable material to the at least oneouter surface; and regulating the temperature of the at least one outersurface to vary the amount of material volatilized. In one aspect,applying a volatilizable material to at least one outer surface of thecylindrical body may comprise exposing the at least one outer surface toa vapor containing a volatilized material; and cooling the at least oneouter surface to condense at least some of the volatilized material fromthe vapor on to the at least one outer surface. In one aspect,regulating the heating of the at least one surface may compriseregulating the flow and/or temperature of a coolant though a passage inthe cylindrical body.

A further aspect of the invention is a treatment chamber valve actuationdevice including an actuation plate; at least one actuation rod mountedto the actuation plate, the at least one actuation rod adapted topenetrate a wall of the chamber and engage a valve mechanism within thechamber; an actuator adapted to displace the actuation plate wherein theplurality of actuation rods are displaced and actuate the valvemechanism; and at least one flexible plate mounted between the actuationplate and the treatment chamber. In one aspect, the at least oneflexible plate may comprise a plurality of flexures mounted between theactuation plate and the treatment furnace.

A still further aspect of the invention is a CIGS photovoltaic cellhaving a low-hydrogen content or substantially no hydrogen content. Inone aspect, the photovoltaic cell may comprise a substrate; and anabsorber deposited on to the substrate, the absorber comprising copper,indium, gallium, and less than 5% hydrogen. In one aspect, the absorbercontains less than 1% hydrogen, or is even hydrogen free. In anotheraspect, the substrate may be a metallic substrate, for example, a steel,stainless steel, or titanium substrate.

These and further aspects of the invention are illustrated in describedwith respect to the attached figures.

BRIEF DESCRIPTION OF FIGURES

The subject matter, which is regarded as the invention, is particularlypointed out and distinctly claimed in the claims at the conclusion ofthe specification. The foregoing and other objects, features, andadvantages of the invention will be readily understood from thefollowing detailed description of aspects of the invention taken inconjunction with the accompanying figures in which:

FIG. 1 is a schematic block diagram of a process for treating a workpiece according to one aspect of the invention.

FIG. 2 is a plot of a heating schedule for the treated work piece andthe treatment material according to one aspect of the invention.

FIG. 3 is a perspective view of a treatment furnace according to anotheraspect of the invention.

FIG. 4 is a front elevation view of the furnace shown in FIG. 3.

FIG. 5 is a right side elevation view of the furnace shown in FIG. 3.

FIG. 6 is a left side elevation view of the furnace shown in FIG. 3.

FIG. 7 is a rear elevation view of the furnace shown in FIG. 3.

FIG. 8 is a top plan view of the furnace shown in FIG. 3.

FIG. 9 is a right side elevation view of the furnace shown in FIG. 3with the right side door removed

FIG. 10 is a detailed side elevation view of a tube assembly as shown asDetail 10 in FIG. 9.

FIG. 11 is a detailed side elevation view of a treatment chamberisolation mechanism shown as Detail 11 in FIG. 10.

FIG. 12A is a right-hand perspective view of the treatment chamberisolation mechanism shown in FIG. 11.

FIG. 12B is a left-hand perspective view of the treatment chamberisolation mechanism shown in FIG. 11.

FIG. 13 is a perspective view of the valve actuating assembly shown inFIG. 9.

FIG. 14 is a side elevation view of the valve actuating assembly shownin FIG. 9.

FIG. 15 is a detailed side elevation view of a heat exchanger shown asDetail 15 in FIG. 10.

FIG. 16A is a perspective view of the tube and heat exchanger assemblyas shown in FIG. 10.

FIG. 16B is a detailed cross section of a conduit mounting shown in FIG.16A.

FIG. 17 is an exploded view of the heat exchanger shown in FIGS. 15 and16A.

FIG. 18A is a perspective view of a furnace assembly according toanother aspect of the invention.

FIG. 18B is a detailed view of one aspect of the furnace assembly shownin FIG. 18A.

FIG. 19 is a left-hand perspective view of a tube furnace assembly shownin FIG. 18A.

FIG. 20 is a front elevation view of the tube furnace shown in FIG. 18A.

FIG. 21 is a right side elevation view of the tube furnace shown in FIG.18A.

FIG. 22 is a left side elevation view of the tube furnace shown in FIG.18A.

FIG. 23 is a cross sectional view of the tube furnace shown in FIGS.18A-22

FIG. 24 is a schematic block diagram of a process for charging thetreatment element to the enclosure according to one aspect of theinvention

FIG. 25 is a plot of treatment element vapor pressure as a function oftemperature.

FIG. 26 is a plot of heat exchanger temperature as a function of coolantflow according to one aspect of the invention.

DETAILED DESCRIPTION OF ASPECTS OF THE INVENTION

The present invention comprises systems, apparatus, and methods thatprovide improved means for fabricating photovoltaic material thatovercome many of the disadvantages of prior art systems and methods.Though aspects of the invention are particularly applicable to thehandling and treatment of photovoltaic materials, aspects of theinvention may be applied to many different photovoltaic andnon-photovoltaic materials.

FIG. 1 is a schematic block diagram of a process 10 for treating amaterial according to one aspect of the invention. The material maycomprise any material that is treated with a gas or vapor, for example,an element-containing vapor. In one aspect, the material comprises aphotovoltaic precursor, for example, a precursor deposited on asubstrate. The treatment gas may comprise any vaporous material.However, in one aspect, the treatment vapor comprises achalcogen-containing vapor, for example, a sulfur-, selenium-, ortellurium-containing vapor; or an indium-, gallium-, orsodium-containing vapor. Though the material being treated may compriseany material or substance, to facilitate the disclosure of theinvention, in some aspects, the material being treated may be referredto as a “work piece.” However, the use of the expression “work piece” isnot intended to limit the scope of the materials to which aspects of theinvention may be applied.

Process 10 includes a series of steps starting with step 12 ofintroducing the work piece to an enclosure, for example, into atreatment oven or furnace, such as treatment furnace illustrated inFIGS. 3 through 9 or FIGS. 18A through 23, though any type ofappropriate treatment furnace may be used. The work piece introduced tothe enclosure may comprise any material that may be treated with a gas,for example, an element-containing vapor. According to one aspect of theinvention, step 12 may be practiced by simply positioning the work pieceon to the bottom surface of an enclosure, on to a support structure (or“boat”), or on to a shelf positioned in an enclosure. However, as willbe discussed below, step 12 may be practiced by positioning one or morework pieces, for example, photovoltaic precursors deposited onsubstrates, into one or more individual, isolated enclosures, forexample, into one or more quartz tubes. These individual, isolatedenclosures permit the operator to individually regulate the treatmentconditions within the individual enclosures, for example, tube, to,among other things, allow the operator to vary or control the treatmentconditions within the enclosure.

In step 14, the work piece is heated to a first temperature fortreatment. One heating schedule that may be used to heat the work pieceis illustrated in FIG. 2. The work piece may be heated to a firsttemperature to raise the work piece at least partially to treatmentelement temperature. FIG. 2 is a plot 30 of a heating schedule curve 32for a work piece and the heating schedule curve 34 and the log of thepartial pressure curve 35 for a treatment element, for example, Se,according to one aspect of the invention. The abscissa 36 of plot 30 isthe time of treatment, typically, in minutes; the left-hand ordinate 38of plot 30 is the temperature, typically, degrees C; and the right-handordinate 39 is the log of the partial pressure of the treatment element.According to heating schedule 32, the temperature of the work pieces maybe increased from ambient temperature, T_(M∞), for example, roomtemperature, for instance, about 20 degrees C., to a first treatmenttemperature, T_(M1), for example, to a temperature greater than 100degrees C. For example, when the work piece being treated is a Cu—In—Gaprecursor, and treatment element is Se, temperature T_(M1) may bebetween about 100 to about 400 degrees C. This rate at which thetemperature may be increased from T_(M∞) and T_(M1) may vary. Forexample, when the work piece being treated is a photovoltaic precursordeposited on a substrate, a slow rise in temperature may prevent theprecursor from cracking and delaminating from the substrate. The rate oftemperature increase may typically be between about 5 degrees C. perminute (° C./m) to about 100 degrees C. per second (° C./s), forexample, about 20° C./m. The work piece to be treated may typically beheld at temperature T_(M1) for at least about 30 seconds to about 90minutes, for example, at least about 30 minutes.

After heating the work piece, the element-containing material, forexample, selenium or sulfur, is heated per step 16, for example, bymeans of the heating schedule illustrated in FIG. 2, to releasetreatment-material-containing vapor into the enclosure. According to oneaspect of the invention, the treatment material is heated independentlyof the heating of the work piece being treated. The temperature of thetreatment material, for example, Se, is elevated to a temperature at orabove the temperature at which treatment material vapor is released, forexample, at or above the vapor temperature at the prevailing pressures.FIG. 2 also illustrates a typical heating schedule 34 for heating thetreatment material. The treatment material may be any material that canbe volatilized upon heating, including materials having multipleelements, that is, compounds. However, to facilitate the disclosure ofthe invention, in the following discussion the treatment material may bereferred to as “the element-containing material” or “the elementcontaining gas or vapor.” It is to be understood that in one aspect ofthe invention an element-containing material or element containing gasor vapor may comprise more than one element, for example, theelement-containing material may be a mixture of elements or a compound.

With reference to FIG. 2, according to one aspect of the invention, thetemperature of the treatment element, as indicated by curve 34, isincreased from an initial temperature T_(E0) to T_(E1). As shown in FIG.2, initial temperature T_(E0) may typically be less than or equal toambient temperature T_(M∞). For example, as will be described more fullybelow in the discussion of the heat exchanger, at the start of thetreatment sequence, the temperature of the treatment element may bemaintained at the temperature of the heat exchanger. Therefore, in oneaspect of the invention, T_(E0) may be less than 60 degrees C., forexample, about 50 degrees C. In one aspect of the invention, the initialtemperature of the treatment element, T_(E0), is kept below thetemperature at which the element begins to volatilize. For example, whenthe treatment element is Se, which begins to volatilize at about 100degrees C., the initial treatment element temperature may be kept below100 degrees C., for example, about 50 degrees C. The temperature T_(E0)may vary broadly, for example, depending upon the vapor pressure of thetreatment element. For example, for materials having high vaporpressures at lower temperatures, the temperature T_(E0) may be less thanroom temperature, for example, even less than 0 degrees C. The rate oftemperature increase from T_(E0) to T_(E1) may vary, but may typicallybe between about 5° C./m to about 100° C./s, for example, about 20°C./m. The treatment element may typically be held at temperature T_(E1)for at least about 30 seconds to about 90 minutes, for example, at leastabout 15 minutes.

According to aspects of the present invention, the timing of theinitiation of the changes in temperature shown in FIG. 2 may varydepending upon the work piece being treated, the treatment element, andthe treatment device being used, among other factors. Specifically, therelative time frame and time sequences of the increases and decreases intemperature may deviate from the relative time frames shown in FIG. 2.For example, though in one aspect shown in FIG. 2, the temperature ofthe work piece 32 may be increased before the temperature of thetreatment element 34 is increased, in one aspect, the temperature of thetreatment element 34 may be increased before or substantially at thesame time as the temperature of the work piece 32 is increased. In oneaspect of the invention, the temperature of the treatment element 34 ismaintained below the temperature of the work piece 32.

In one aspect, after holding the treatment element at temperature T_(E1)for about 15 minutes, the temperature of the treatment element may beincreased to a temperature T_(E2), for example, for Se, T_(E2) may beabout 100 to about 400 degrees C. The rise in temperature from T_(E1) toT_(E2) may be between about 5° C./m to about 100° C./s, for example, atleast about 20° C./m. The treatment element may typically be held attemperature T_(E2) for at least about 30 seconds to about 90 minutes,for example, at least about 30 minutes.

With reference again to FIG. 1, after heating the treatment element torelease a treatment element-containing vapor into the enclosure per step16, the one or more work pieces are exposed to the treatment elementvapor, per step 18, whereby at least some of the work pieces are treatedwith the treatment element. Treating the work piece with theelement-containing vapor may comprise reacting the element with the workpiece or providing an overpressure of the element-containing vapor tothe work piece. In one aspect, providing an overpressure comprisesproviding a vapor pressure of the element-containing vapor, for example,Se vapor, that is greater than the vapor pressure of the element, forexample, Se, present in the work piece. This overpressure may minimizeor prevent the volatilization and the net loss of element from the workpiece. Step 18 may simply be practiced by allowing the work piecespositioned in the enclosure to be exposed to the treatment element vaporfor a predetermined time periods, for example, 5 seconds to 5 hours. Thetreatment time for which the work piece is exposed to the elementcontaining vapor may typically range from about 30 seconds to about 90minutes.

As shown in FIG. 2, while the treatment element is held at temperatureT_(E2), the temperature of the work piece being treated, as indicated bycurve 32, may be increased, for example, rapidly, from temperatureT_(M1) to T_(M2), for instance, to a temperature where the treatmentelement begins to react with the treated material, for example, at atemperature of about 400 to about 600 degrees C. Se reacts rapidly witha Cu—In—Ga matrix to form a Cu—In—Ga—Se matrix. The rise in temperatureof the treated material from T_(M1) to T_(M2) may be at a rate ofbetween about 5° C./m to about 100° C./s, for example, about 20.0° C./m.Shortly thereafter, the temperature of the treatment element, forexample, Se, is increased from T_(E2) to T_(E3) to enhance thevolatilization of the treatment element and release sufficient vaporoustreatment element to complete the reaction. For example, for Se, thetemperature T_(E3) may be about 200 to about 550 degrees C. The rise intemperature of the treatment element from T_(E2) to T_(E3) may be at arate of between about 5° C./m to about 100° C./s, for example, about 20°C./m. The treated work piece may be held at temperature T_(M2) toprovide for sufficient reaction of the treatment element with thetreated work piece. This treatment time may be at least about 30 secondsto 90 minutes.

With reference to FIG. 1, in step 20, upon completion of the treatmentof the work piece, the temperature of the treatment element is reduced,for example, by active cooling, for instance, by means of a cooling heatexchanger. According to one aspect of the invention, the reduction ofthe treatment element temperature substantially terminates the releaseof treatment-element-containing vapor from the treatment element, forexample, the Se. The reduction of the treatment element temperature mayalso allow at least some of the treatment-element-containing vapor tocondense onto the treatment element. In one aspect, substantially all ofthe treatment element vapor may condense onto the treatment element, forexample, whereby the loss of treatment element to, for example,condensation onto the enclosure, is minimized. According to one aspectof the invention, due to this condensation or “recapture” of treatmentelement, the utilization rate of the treatment element, for example, Seor S, is very high. For example, in one aspect utilization rate is atleast about 90% or more, in some instances at least about 95% or more.This temperature reduction of the treatment element is shown as curve 34in FIG. 2.

Again, with reference to FIG. 1, before, during, or after the practiceof cooling the treatment element per step 20, the temperature of thework piece being treated may be reduced as indicated by step 22 inFIG. 1. Upon cooling, the treated work pieces may be further handled orprocessed as desired. The cooling of the work pieces may be practicedactively, for example, by means of a cooling heat exchanger and/orforced convection, or through unforced, natural convection and/orradiation.

This decrease in the temperature of the treated work piece is also shownin FIG. 2. As indicated by curve 32, the temperature of the treated workpiece is cooled, for example, slowly, from T_(M2) to about roomtemperature. This cooling may be practiced to prevent damage to the workpiece; for example, when the work piece is a photovoltaic material,cooling is carried out relatively slowly to prevent cracking of the workpiece or delamination from the substrate. The rate of cooling may rangefrom between about 5° C./m to about 100° C./s, for example, about 5.0°C./m.

As shown in FIG. 2, before, during, or after the treated work piece isbeing cooled to room temperature, the treatment element is cooled fromtemperature T_(E3) to a lower temperature per curve 34, for example, toa temperature below the temperature at which the element volatilizes.When the treatment element is Se, the Se is cooled to a temperaturebelow 100 degrees C., for example, to a temperature of about 50 degreesC. The rate of cooling may range from between about 5° C./m to about100° C./m, for example, about 15.0° C./m. Again, the curves in FIG. 2are representative of the invention, for example, sulfur volatilizes ata lower temperature, and tellurium volatilizes at a higher temperature.

In one aspect of the invention, the rapid cooling of the treatmentelement typically causes the vaporous element to recondense upon thecooled element whereby loss of the element to condensation on thesurfaces of the furnace or associated surfaces is minimized orprevented. Thus, by controlled cooling of the treatment element, more ofthe treatment element is retained, for example, for further treatment.

FIG. 2 also displays a typical corresponding variation in the log of thepartial pressure curve 35 of a treatment element as the temperature ofthe treatment element 34 varies. As shown, the partial pressure 35tracks the changes in the temperature 34 very closely. For example, fora Se treatment element, at a temperature T_(E2) of the Se of about 100to about 400 degrees C., the partial pressure of the Se is about 5.0Torr at about 400 degrees C. Also, for a Se temperature T_(E3) of about200 to about 550 degrees C., the partial pressure of the Se can be ashigh as about 80 Torr. The partial pressure curve 35 is a usefulparameter in controlling the operation of the cooling heat exchanger orcondenser/evaporator, as will be discussed more thoroughly below.

As shown in and described above with respect to FIG. 2, in one aspect ofthe invention, the temperature of a work piece to be treated and thetemperature of a volatile element with which the work piece is to betreated with are independently controlled to optimize the reaction, forexample, to improve reaction selectivity and/or reaction kinetics, andalso to minimize the loss of treatment element, for example, sulfur orselenium. According to process 10 shown in FIG. 1 and the heatingschedules shown in FIG. 2, a work piece may be treated with treatmentelement in a controlled environment whereby the release of treatmentelement is regulated to optimize the treatment and minimize the loss oftreatment element. In one aspect, method 10 or sub-sequences of method10 of FIG. 1 may be practiced repeatedly. For example, steps 14, 16, 18,and 20 may be practiced at least twice, possibly three or more times, toeffect the desired treatment of the work piece. Also, steps 18 and 20may be practiced at least twice (possibly three or more times), forexample, before proceeding with step 22, to effect the desired treatmentof the work piece.

The process 10 shown in FIG. 1 may also include the optional steps ofcharging the enclosure with treatment element 24 and cooling thetreatment element 26 prior to or during the heating step 14. Theseoptional steps are shown in phantom in FIG. 1. According to one aspectof the invention, the treating element may be introduced, or “charged,”24 to the enclosure before the work piece to be treated is introduced tothe enclosure 12. This charging of the treatment element may bepracticed by the steps illustrated in FIG. 24 and will be discussedbelow. The cooling step 26 may be practiced to prevent theelement-containing material from volatilizing prematurely, that is,before the work piece is ready to be treated.

The method of the invention may be practiced in any suitable enclosurethat can be adapted to regulate the temperature of the work pieces andthe treatment material, for example, independently regulated. Oneenclosure that may be used to practice aspects of the invention isillustrated in FIGS. 3 through 9 and FIGS. 18A through 23. To those ofskill in the art, the term “furnace” is sometimes reserved for devicesin which work pieces are heated to temperatures of at least 1200 degreesC. while the term “oven” is sometimes reserved for devices in which workpieces are heated to temperatures of between about 200 degrees C. toabout 300 degrees C. However, the use of the terms “furnace” or “oven”in the following discussion is not intended to limit the scope of theinvention to these temperature ranges. Aspects of the present range maybe used to heat work pieces in these and other temperature ranges, forexample, as low as room temperature, for example, 20 degrees C., to ashigh a temperature that does not impact the performance or integrity ofthe disclosed devices, for example, at least 2000 degrees C.

FIG. 3 is a perspective view of a treatment furnace 50 according to oneaspect of the invention. Treatment furnace 50 may be used to practicethe invention illustrated in and described with respect to FIGS. 1 and2. FIG. 4 is a front elevation view of furnace 50 shown in FIG. 3. FIG.5 is a right side elevation view of the furnace 50 and FIG. 6 is a leftside elevation view of furnace 50. FIG. 7 is a rear elevation view offurnace 50 and FIG. 8 is a top plan view of furnace 50 shown in FIG. 3.According to aspects of the invention, furnace 50 (and furnace 200discussed below) are specially designed to operate under a broad rangeof operating conditions. For example, furnace 50 (and 200) may beoperated under a broad range of temperatures, for example, from 0 to2000 degrees C., and a broad range of pressures, for example,super-atmospheric pressures to sub-atmospheric pressures. For instance,furnace 50 (and 200) may be specially designed to operate under a vacuumranging from just below about 1 standard atmosphere to 10⁻⁶ Torr.

As shown in FIGS. 3 through 8, furnace 50 includes a front door assembly52, a right side door assembly 54, a left side door assembly 56, a rearpanel assembly or back 58, a top 60, and a bottom 62. Furnace 50 may bemounted on a plurality of support legs 64. As shown in FIGS. 3 and 4,front door assembly 52 may be pivotally mounted to the furnace 50 byhinge assembly 66 and may comprise a plate 53 having appropriatereinforcing elements 55, for example, structural tubing or angles.Reinforcing elements 55 may also comprise conduits through which aheating or cooling medium may be passed to either heat or cool furnace50. Plate 53 may also be heated and cooled by other means. Front doorassembly 52 may include valve-actuating assembly 68 mounted to plate 53.Valve actuating assembly 68 may be adapted to actuate one or moreisolation valves mounted within furnace 50. (See FIGS. 13 and 14 andtheir description for details of valve-actuating assembly 68.) Frontdoor assembly 52 may typically provide means for opening furnace 50 toservice furnace 50 or load work pieces, for example, photovoltaicmaterial precursors, into furnace 50 for treatment. Front door assembly52 may typically include a handle and locking assembly 57 for opening,closing, and securing front door assembly 52.

As shown in FIGS. 3 and 5, right side door assembly 54 of furnace 50 maycomprise a plate 57 having appropriate reinforcing elements 59, forexample, structural tubing or angles. Reinforcing elements 59 may alsocomprise conduits through which a heating or cooling medium may bepassed to either heat or cool furnace 50. Plate 57 may also be heatedand cooled by other means. Though right side door assembly 54 may berigidly mounted to furnace 50 (that is, not adapted to be opened), asshown in FIG. 3, right side door assembly 54 may be removably mounted tofurnace 50, for example, pivotally mounted to furnace 50 by means ofhinge assembly 70. Right side door assembly 54 may be secured to furnace50 by conventional means, for example, by means of mechanical fastenersor welding, such as, clamps 72. Clamps 72 may be conventional clampsadapted to secure right side door assembly 54. Right side door assembly54 may typically provide means for opening furnace 50 for servicing, forexample, servicing the work piece support structures, and relatedtreatment devices, for example, the valves, heat exchangers, or heaters,discussed below.

As shown in FIGS. 3 and 6, left side door assembly 56 of furnace 50 maybe similar in construction to right side door assembly 54 and maycomprise a plate 67 having appropriate reinforcing elements 69, forexample, structural tubing or angles. Again, reinforcing elements 69 mayalso comprise conduits through which a heating or cooling medium may bepassed to either heat or cool furnace 50. Plate 67 may also be heatedand cooled by other means. Left side door assembly 56 may also berigidly mounted to furnace 50 (that is, not adapted to be opened).However, as shown in FIG. 6, left side door assembly 56 may be removablymounted to furnace 50, for example, pivotally mounted to furnace 50 bymeans of hinge assembly 80. Left side door assembly 56 may be also besecured to furnace 50 by conventional means, for example, by means ofmechanical fasteners or welding, such as, clamps 73. Clamps 73 may besimilar to clamps 72 provided on the right side door assembly 54 shownin FIGS. 3 and 5. Left side door assembly 56 may typically also providemeans for opening furnace 50 for servicing, for example, servicing thework piece support structures, and related treatment devices, forexample, the valves and heat exchangers, discussed below.

FIG. 7 illustrates the rear panel assembly 58 of furnace 50 which maycomprise a plate 97 having appropriate reinforcing elements 99, forexample, structural tubing or angles. Reinforcing elements 99 may alsocomprise conduits through which a heating or cooling medium may bepassed to either heat or cool furnace 50. Plate 97 may also be heatedand cooled by other means. Rear panel assembly 58 may also be rigidlymounted to furnace 50, that is, not adapted to be opened, but may alsobe removable, for example, pivotally mounted to furnace 50 by means ofhinge assembly. As shown in FIG. 7, rear panel assembly 58 may also besecured to furnace 50 by conventional means, for example, by means ofmechanical fasteners or welding.

In aspects of the invention, furnace 50 may include various access portsor openings for assorted purposes, for example, for introducing orremoving process fluids (that is, liquids and/or gases), introducing orremoving heating or cooling fluids, applying a vacuum, or providingpathways for wiring, cabling, or instrumentation, among other reasons.As shown in FIGS. 3 through 8, access ports or openings may be locatedin front door assembly 52, right side door assembly 54, left side doorassembly 56, rear panel assembly 58, top 60 or bottom 62. As shown inFIG. 7, according to one aspect, rear panel assembly 58 may include aplurality of access ports, including a first row 100 of flanged ports102 on the left side of rear panel 58 and a second row 104 of flangedports 106 on the right side of rear panel 58. Ports 102 in row 100 andports 104 in row 102 may provide ports providing power, such as toheating elements 88; or for instrumentation wiring, such as totemperature or pressure sensors. As also shown in FIG. 7, rear panel 58may also include two rows 108 of ports 110 centrally mounted on rearpanel 58. Ports 110 may be mounted in a common plate 112 and be mountedto plate 97 of rear panel 58 by a plurality of mechanical fasteners 114,for example, bolts or screws. According to one aspect of the invention,ports 110 may provide conduits for venting, purging, or introducingprocess or control fluids to furnace 50. For example, in one aspect,ports 110 may provide cooling or heating fluid (for example, liquid orgas) to an internal component, such as, to a heat exchanger (forexample, heat exchanger 86 shown in FIGS. 15 and 16A).

The top assembly 60 of furnace 50 is illustrated in the top plan view ofFIG. 8. Top assembly 60 may comprise a plate 117 having appropriatereinforcing elements 119, for example, structural tubing or angles.Again, reinforcing elements 119 may also comprise conduits through whicha heating or cooling medium may be passed to either heat or cool furnace50. Plate 117 may also be heated and cooled by other means. Top assembly60 may also be rigidly mounted to furnace 50, that is, not adapted to beopened, but may also be removable, for example, pivotally mounted tofurnace 50 by means of a hinge assembly (not shown). As shown in FIG. 8,top assembly 60 may also be secured to furnace 50 by conventional means,for example, by means of mechanical fasteners or welding. As shown inFIG. 8, top assembly 60 may include a plurality of access ports,including a first row 120 of flanged ports 122 on the left side of topassembly 60 and a second row 124 of flanged ports 126 on the right sideof top assembly 60. Ports 122 in row 120 and ports 124 in row 122 mayprovide access ports for power, instrumentation, venting, purging, orprocess fluids, among other functions. As also shown in FIG. 8, topassembly 60 may also include one or more flanged ports 130, for example,a centrally mounted port in top assembly 60. Ports 130 may also providean access for ports for power, instrumentation, venting, purging, orprocess fluids or simply provide a access for flushing or purgingfurnace 50.

As shown in FIGS. 3 through 8, a plurality of access ports may also belocated in bottom 62. Similar to top 60, bottom 62 may include first row132 of flanged ports 134 on the left side of bottom assembly 62 and asecond row 136 of flanged ports 138 on the right side of bottom assembly62. Ports 134 in row 132 and ports 138 in row 136 may also provideaccess to the inside of furnace 50 for providing purging, venting,process fluids, or instrumentation. Bottom 62 may also include one ormore flanged ports 140 centrally mounted in bottom 62. Port 140 may alsoprovide an access for ports for power, instrumentation, venting, orprocess fluids or simply provide a access for flushing or purgingfurnace 50.

FIG. 9 is a right side elevation view of the furnace 50 shown in FIGS. 3through 8 with the right side door assembly 54 and hinge assembly 70removed to reveal the internal structure of furnace 50. As shown in FIG.9, furnace 50 includes at least one work piece treatment assembly 81,but typically includes a plurality of work piece treatment assemblies 81mounted in furnace 50. FIG. 10 is a detailed side elevation view of onework piece treatment assembly 81 as shown as Detail 10 in FIG. 9. In oneaspect of the invention, work piece treatment assemblies 81 may bemounted front door assembly 52, right side door assembly 54, left sidedoor assembly 56, rear panel assembly 58, top 60, or a bottom 62. Forexample, in one aspect, the work piece treatment assemblies 81 may bemounted as rack on a door or side of furnace 50 whereby one or moretreatment assemblies 81 may be manipulated or handled, for example,removed or installed, by means of a door or side of furnace 50.

As shown in FIG. 10, each treatment assembly 81 includes a treatmentchamber, container, or tube 82; an isolation apparatus (or “flappervalve”) assembly 84; and a material delivery (or “condenser/evaporator”)assembly 86. Tubes 82 are adapted to accept one or more work pieces 90,for example, a photovoltaic precursor material, to be treated. Accordingto aspects of the invention, work piece 90 is positioned in tube 82 andisolated from the rest of furnace 50 whereby the treatment environmentwithin tube 82 can be controlled as desired, for example, at a desiredtemperature, pressure, and/or vapor content. The isolation of tubes 82from the rest of furnace 50 minimizes the exposure of the rest offurnace 50 to gases and vapors present in tubes 82, for example, toxicgases and vapors. According to one aspect of the invention, the use ofone or more tubes or inner enclosures 82 inside an outer enclosure, forexample, as provided by the walls of chamber 50, isolates the hottreatment zone of the inner enclosure from the outer enclosure wherebylow temperature sealing devices, for example, elastomeric seals, may beused to seal the outer enclosure from the ambient environment andminimize thermal damage to the sealing devices. It will be apparent tothose of skill in the art that aspects of the invention provide enhancedfunctionality and enhanced throughput compared to prior art devices andmethods.

As shown in FIG. 10, furnace 50 includes a plurality of heat sources 88adapted to heat the one or more work pieces 90 in tube 82. Heat sources88 may be an infrared heat source, an inductive heat source, or aconvective heat source. For example, heat source 88 may be an infraredheating lamp. Tube 82 is typically fabricated from a material thatreadily permits the heating of work piece 90 by means of heat sources88, for example, is made from a transparent or translucent material,such as, quartz, stainless steel (such as 316 stainless steel) or acorrosion-resistant alloy, such as a Hastelloy® alloy. Heat sources 88may be mounted to the sides, roof, or floor of furnace 50 or mounted toa perforated mounting plate (not shown) having apertures sized toreceive and support heat sources 88. Tube 82 may assume any appropriatecross-sectional shape, such as round, rectangular, and square, forexample, depending upon the size and shape of the work piece beingtreated and the size and shape of furnace 50. A perspective view of onetube 82 that may be used in one aspect of the invention is shown in FIG.16A. As shown in FIG. 10, tube 82 may be mounted on one or more supports92, for example, one or more bars or support tubes mounted horizontallyin furnace 50. Supports 92 may also be fabricated from a material thatreadily permits the heating of work piece 90 by means of heat sources88, for example, is made from a transparent or translucent material,such as, glass or quartz. Tube 82 may be rigidly mounted to supports 92or may be allowed to translate on supports 92, for example, to permitease of handling, for instance, removal, of tubes 82 from furnace 50,for instance, through open rear panel assembly 58. Supports 92 may bemounted to the sides, roof, or floor of furnace 50 or mounted to aperforated mounting plate (not shown) having apertures sized to receiveand support supports 92, for example, the same mounting plate adapted tosupport heat sources 88. Temperature sensing devices, for example,thermocouples, may be mounted in tubes 82 and/or supports 92.

FIG. 11 is a detailed side elevation view of a tube sealing assembly 84shown as Detail 11 in FIG. 10. FIG. 12A is a right-hand perspective viewof tube sealing assembly 84 shown in FIG. 11. FIG. 12B is a left-handperspective view of the tube sealing assembly 84 shown in FIG. 11.

As shown in FIGS. 11, 12A, and 12B, sealing assembly 84 is adapted toclose or seal the end of treatment chamber or tube 82 (shown inphantom). The sealing assembly 84 includes a sealing or “flapper valve”assembly 180 and means 182 for compressing the sealing assembly 180against the treatment chamber or tube 82. Though in some aspects thesealing assembly 180 may provide an vapor-tight cover to the one or moretreatment chambers 82, in another aspect, the engagement of sealingassembly 180 may not be vapor-tight, but may simply minimize the escapeof fluids (that is, gases or liquids) from treatment chamber 82 duringtreatment. The sealing assembly 180 includes a support structure 184, atleast one cover plate 186 adapted to engage the treatment chamberopening, and a plurality of rods 188. The plurality of rods 188 have afirst end 190 mounted to support structure 184, for example, resilientlymounted to support structure 184, and a second end 195 adapted to engagecover plate 186.

Support structure 184 may be any support structure adapted to supportthe one or more cover plates 186 and adapted to engage the means 182 forcompressing the sealing assembly 180 against the treatment chamber ortube 82 while withstanding the treatment temperatures, for example, upto 800 degrees C. In one aspect, support structure 184 may be a singleplate, for example, a plate having sufficient stiffness that does notrequire the need for additional structural support bars or ribs. Inanother aspect, support structure 184 may comprise a plurality of plates192, for example, a plurality of vertically or horizontally orientedplates. Plates 192 may be attached by means of mechanical fasteners,welding, or by common support bars or ribs. In the aspect shown in FIG.11, support structure 184 may comprise a plurality of horizontal plates192 mounted to a plurality of vertical support bars 194. Plates 192 maybe mounted to bars 194 by mechanical fasteners or welding. Plates 192may include holes or slots 193 through which mechanical fasteners (notshown) may adjustably engage support bars 194.

As shown in FIGS. 11 and 12A, plates 192 include a plurality ofapertures 197 through which the first ends 190 of rods 188 pass throughplates 192. Rods 188 may be mounted to plates 192 by conventional means,for example, by means of mechanical fasteners. As shown in FIGS. 11 and12B, in one aspect, rods 188 may mount to plates 192 by means of aflexural member 199 and one or more fasteners 201, for example, one ormore hex nuts. (Though not shown in FIG. 12B, rod 188 may be retained toflexural member 199 by a second fastener, for example, a hex nut locatedbehind flexural member 199.) Flexural member 199 may comprise a“flexure” as discussed below. Flexural member 199 may include a circulardisk section 203 and an elongated stem 207. Disk section 203 may besized to ensure that disk section 203 cannot pass through aperture 197in plate 192. Stem 207 may be mounted to plate 192 by conventionalmeans, for example, by clamp plate 209 and fasteners 216. According toone aspect of the invention, the flexibility of flexural member 199provides for at least some alignment for the positioning of plate 186 ontube enclosure 82. For example, flexural member 199 and pin 208 mayprovide a parallel flexure configuration that minimizes the misalignmentof plate 186 while providing at least some resiliency or compliance inthe alignment of the mating structures.

As shown in FIGS. 11, 12A, and 12B, plates 192 may include an extension196, for example, plates 192 and extensions 196 may comprise structuralangles. Extension 196 may be solid or include a plurality of throughholes 198, for example, to facilitate assembly, to reduce the weight ofsupport structure 184, or to provide a purge path to eliminate virtualleaks. Plates 192, bars 194, and extensions 196 may be made from anymetal or non-metal structural material, for example, a steel, stainlesssteel, titanium, nickel, or any other structural metal. In one aspect,plates 192, bars 194, and extensions 196, may be made from stainlesssteel, for example, 304 stainless steel.

The one or more cover plates 186 may be metallic, but are typically madefrom stainless steel sheet having a thickness of from about 0.005 inchesto about 0.125 inches. The size of cover plate 186 will vary dependingupon the size of the treatment chamber and the treatment chamberssealing assembly 180 used to seal the treatment chamber. Cover plates186 may be about 3 inches long to about feet long and may have a widthfrom about 1 inch to about 1 foot. Typically cover plate 186 is about 2feet long and about 2 inches in width. In one aspect of the invention,cover plate 186 may engage a single or a plurality of treatmentchambers, for example, 2, 3, or more treatment chambers. That is, coverplate 186 may be adapted to seal a plurality of treatment chamberopenings, for example, a plurality of tubes 82.

Rods 188 are adapted to transmit a load from support assembly 184 to thecover plates 186. Rods 188 may have any cross section, including squareor rectangular, but are typically circular in cross section and may havea diameter of between about 0.125 inches and 0.5 inches. Rods 188 aretypically about 0.375 inches in diameter and may be at least partiallythreaded. Rods 188 may engage plates 186 by conventional means, forexample, by means of mechanical fasteners or welding. However, in oneaspect, a first end 195 of rods 188 is not rigidly mounted to plates 186but may be flexibly engaged to allow for some relative displacementbetween rods 188 and plates 186. One means of providing this non-rigidengagement to the first end 189 of rod 188 is illustrated in FIG. 12B,where first end 195 engages plates 186 by means of clips 200. As shownin FIG. 12B, clip 200 may comprise a central u-shaped portion 219 and atleast one, typically, two, cantilevered plate sections 221. Cantileveredplate sections 221 may comprise “flexures” as discussed below. Platesections 221 may have at least one, typically, two, holes (not shown)adapted to engage and retain the first end 195 of rods 188, for example,by means of one or more fasteners 217, for example, hex nuts threaded torods 188. Clip 200 may be mounted to plate 186 by mechanical fastenersor welding, for example, simple resistance welding at section 219. Clip200 is typically also made from stainless steel, for example, 304stainless steel.

As discussed above, the second end 190 of rod 188 is adapted to engagesupport structure 180. As shown in FIG. 11 and 12B, second end 190 maypass through at least one hole 197 in plate 192 and, for example, engageflexural member 199. As also shown in FIG. 11 and 12B, rod 188 mayinclude a resilient mounting to plate 192, for example, by means of oneor more springs 204, for example, coil springs. Springs 204 arepreferably made from a temperature resistant material, for example, ahigh strength austenitic nickel-chromium-iron alloys, for instance, aSpecial Metals Corporation's Inconel® alloy, such as Inconel® 750 alloy,or its equivalent. Rod 188 may include one or more spring capturing orretaining devices, for example, a cup-like spring retaining device 206mounted to rod 188. In this aspect, retaining device 206 receivessprings 204 to promote engagement between spring 204 and rod 188.Retaining device may also include a sleeve 223 (see FIG. 11) thoughwhich rod 188 passes. In one aspect, the end of sleeve 223 may provide asurface against which fastener 201 captures flexural member 199 whenattaching flexural member 199 to rod 188. Plates 192 may also include arecess or counter bore 222 (see FIG. 11) for receiving spring 204 tofacilitate assembly and ensure alignment during operation. Rods 188 andretaining devices 206 may be made from any metal or non-metal structuralmaterial, for example, a steel, stainless steel, titanium, nickel, orany other structural metal. In one aspect, rods 188 and retainingdevices 206 may be made from stainless steel, for example, 304 stainlesssteel.

In one aspect, sealing assembly 84 may include additional supportmembers for rods 188, for example, to position rods 188 and cover plates186 in the desired position to engage treatment chambers 82. As shown inFIG. 11, sealing assembly 184 may include one or more retaining members,pins, or bars 208 to support rods 188. In one aspect of the invention,bars 208 may comprise “flexures” as discussed below. Bars 208 may bemounted to any convenient location on support structure 180 and engagerods 188 by conventional means, for example, mechanical fasteners. Inthe aspect shown in FIG. 11, bars 208 are mounted to extension 196 (forexample, to the leg of the structural angle) by means of mechanicalfasteners and a clamp plate 210. Bars 208 may be mounted to rods 188 byconventional means, including welding or mechanical fasteners. As alsoshown, bars 208 may be mounted to rods 188 by capture between two ormore fasteners 312, for example, hex nuts, threaded to rod 188. It willbe apparent to those of skill in the art that the threaded mounting ofbar 208 to rod 188 via nuts 312 permits the assembler to vary theposition of engagement whereby the elevation of rods 188 (and of plates186) may be varied as desired.

According to aspect of the invention, the sealing assembly 84illustrated in FIGS. 11 and 12 is displaced into engagement with one ormore treatment chambers or tubes 82 to at least partially limit theescape of fluids from treatment chamber 82 during treatment. Thedisplacement of sealing assembly 84 into engagement with treatmentchambers 82 is effected by means of valve-actuation assembly 68 (seeFIGS. 3-5 and 9). Though valve-actuation assembly 68 may be positionedwithin furnace 50 or outside of furnace 50, in the aspect shown in FIGS.3-5, valve-actuation assembly 68 is positioned outside of furnace 50 andis adapted to engage sealing assembly 84 by means of a plurality of rodsextending through a wall of furnace 50.

FIG. 13 is a perspective view of valve actuation assembly 68 shown inFIG. 9. FIG. 14 is a side elevation view of the valve actuation assembly68 shown in FIG. 9. As shown, valve actuation assembly 68 is mounted tofront door plate 53 by means of a structural support 218 and is adaptedto displace at least one actuation rod 220, typically, a plurality ofrods 220. In the aspect shown, six actuation rods 220 are displaced byvalve actuation assembly 68. Valve actuation assembly 68 includes one ormore linkage assemblies 224, for example, a spherical linkage assembly,mounted to door 53 and a piston assembly 234 mounted to structuralsupport 218 and to linkage assembly 224. According to the presentinvention, piston assembly 234 displaces structural support 218 to whichrods 220 are mounted to displace rods 220 and sealing assembly 84 (seeFIGS. 11 and 12).

As shown in FIG. 14, linkage assembly 224 includes a body 228, a firstbracket 230 by which body 228 is mounted to piston assembly 234 and asecond bracket 232 mounted to plate 233 which is mounted to door plate53, for example, by conventional mechanical fasteners or welding. One ormore pneumatic or hydraulic lines (not shown) may be provided to actuatepiston assembly 234. Hydraulic or pneumatic cylinder 234, for example, ashort-stroke cylinder, mounted to support structure 218.

Support structure 218 may include a variety of structural elements fortransmitting the displacement provided by piston assembly 224 to rods220. Piston assembly 224 is mounted to main plate 236 of supportstructure 218 to which the plurality of rods 220 are mounted. Main plateor actuation plate 236 may take a variety of shapes depending upon thesize and number of rods 220 to which main plate 236 is mounted. In theaspect shown in FIG. 13, main plate 236 takes the general form of theletter “H” where the rods 220 are mounted to the uprights and the pistonassembly 224 mounts to the cross beam. In one aspect, the main plate 236may be relatively stiff, for example, at least about 0.375 inches inthickness, to promote uniform displacement of rods 220, for example, tominimize misalignment of rods 220. In one aspect, main plate 236 mayinclude one or more reinforcing ribs to increase the stiffness of plate236.

Support structure 218 may also include at least one flexural plate 238,240 mounted to main plate 236. In one aspect, plates 238 and 240comprise flexures, that is, precision flexural elements that can controlthe accuracy of deflection, for example, parallel flexures. (See Slocum,Precision Machine Design (1992), the disclosure of which is incorporatedby reference herein.) Flexural plates 238 and 240 not only support themain plate 236 and rods 220, but flexural plates 238 and 240 may alsoprovide at least some flexibility to support structure 218 whereby rods220 can be more uniformly displaced. Flexural plates 238 are mounted tomain plate 236 by mounts 242. Mounts 242 may assume a variety of shapesand sizes, but, as shown in FIGS. 13 and 14, mounts 242 may comprise acenter plate 244, a base plate 246 mounted to the center plate, and twogussets 248 mounted to the sides of the center plate. Mounts 242 may befabricated by welding or mechanical fasteners. Flexural plates 238 maybe mounted to mounts 242 by a mounting plate 250 and mechanical fasters.

Flexural plates 238 are also mounted to furnace 50, for example, to thefront door plate 53, by any conventional mounting means. As shown inFIGS. 13 and 14, flexural plates 238 may be mounted to furnace 50 viaflanged support 252. As shown in FIG. 14, flanged support 252 mayinclude a center web plate 254 and a flange plate 256. Flanged supports252 may be mounted to furnace 50 by conventional means, for example,mechanical fasteners or welding. Flexural plates 238 may be mounted toflanged support 252 by a mounting plate 250 and mechanical fasters.

Flexural plates 240 may also be mounted to main plate 236 by mounts 252,that is, structural members similar to or identical to mounts 242discussed above. Flexural plates 240 may be mounted to mounts 252 by amounting plate 250 and mechanical fasteners. Flexural plates 240 arealso mounted to furnace 50, for example, to the front door plate 53, byany conventional mounting means. As shown in FIGS. 13 and 14, flexuralplates 240 may be mounted to furnace 50 via plates 254. As shown in FIG.13, plates 254 may be mounted to furnace 50 by conventional means, forexample, mechanical fasteners or welding. Flexural plates 240 may bemounted to plates 254 by a mounting plate 250 and mechanical fasters.

According to one aspect of the invention, the function of valveactuation assembly 68 is to displace sealing assembly 84 against thetreatment tubes 82. This displacement of sealing assembly 84 istypically effected via rods 220. As shown in FIG. 14, rods 220 aremounted to main plate 236. Rods 220 may be mounted to plate 236 byconventional mechanical fasteners, for example, as shown in FIG. 14,rods 220 are mounted to plate 236 by a pair of collars 280 and 281. Rod220 extends into furnace 50 through flange 282 and flanged bellowsassembly 284. Bellows assembly may provide some flexibility to theinsertion of rods 220 into furnace 50. Bellows assembly 284 includes abellows 286 and two flanged pipes 287 and 288. Bellows assembly 284 maybe a typical off-the-shelf item. According to one aspect, rods 220 maybe rigidly mounted to flange 282, for example, by mechanical fastenersor welding, whereby the displacement of rods 220 is accompanied by thedisplacement, for example, compression, of bellows 286. Flanged pipe 288is mounted to a flanged nipple 290 mounted to front door plate 53. Theflanged connections may typically comprise “conflat” flanges, forexample, conflat flanges provided by the Kurt J. Lesker Company ofClairton, Pa., or their equivalent. ISO and/or ASA flange systems mayalso be used. After passing through front door plate 53, rods 220 engagesealing assembly 84. Rods 220 may engage sealing assembly 84 in anyfashion effective to displace sealing assembly 84. In one aspect, rods220 are mounted to support structure 184 of sealing assembly 84 bymechanical fasteners, for example, by bolts or screws, to plates 192 orbars 194 (see FIGS. 11 and 12) of support structure 184. Rods 220 mayalso be welded to support structure 184.

FIG. 15 is a detailed side elevation view of a heat exchanger orcondenser/evaporator 86 shown as Detail 15 in FIG. 10. A perspectiveview of heat exchanger 86 along with tube 82 is shown in FIG. 16A. FIG.16B is a detailed cross section of the conduit mounting shown in FIG.16A. FIG. 17 is an exploded view of heat exchanger 86 shown in FIGS. 15and 16A. According to aspects of the invention, heat exchanger 86 (andany other heat exchanger identified herein) may be a device thatexchanges heat between the body of the device and a working fluidpassing through the device to vary the temperature of at least onesurface of the device. In one aspect of the invention, heat exchanger 86(and any other heat exchanger identified herein) may function as a“condenser,” that is a device having at least one surface upon which avolatilized material may condense upon, for example, by lowering thetemperature of the surface. In one aspect of the invention, heatexchanger 86 (and any other heat exchanger identified herein) mayfunction as an “evaporator,” that is, a device having at least onesurface upon which a volatilizable material is applied and from whichthe volatilizable material may be volatilized or “evaporated,” forexample, by raising the temperature of the surface. In another aspect ofthe invention, heat exchanger 86 (and any other heat exchangeridentified herein) may function as both a “condenser” and an“evaporator,” and may be referred to as a “condovator.”

As shown in FIGS. 15-17, tube 82 comprises a main cylindrical section83, an open first end having a first flange 85, and open second endhaving a second flange 87. Heat exchanger 86 is mounted to flange 87 ofthe open second end of tube 82 wherein a surface of heat exchanger 86 isexposed to the open end of tube 82. In one aspect of the invention heatexchanger 86 may comprise a material delivery device, that is, a devicefor use in regulating the delivery of a vaporous material or element,for example, vaporous Se or S, to tube 82. As shown in FIGS. 15-17, heatexchanger 86 consists of an elongated cylindrical body 150 having atleast one surface 151 exposed to the open end of tube 82. According toone aspect of the invention, surface 151 is adapted to receive at leastsome volatilizable element, for example, by means of the “charging”process described below. The temperature of surface 151 is thenregulated, for example, heated or cooled, whereby the elementvolatilizes and the vaporous element is released into tube 82 to treatwork piece in tube 82.

Cylindrical body 150 of heat exchanger 86 may be a rectangular, square,or circular cylindrical body, or any other shaped cylindrical bodyadapted to be mounted to a treatment tube, such as, treatment tube 82.Cylindrical body 150 may include at least one first passage 152, forexample, a circular passage, extending the substantially the entirelength of body 150, and two smaller passages, 154 and 156, for example,also circular, and also extending substantially the entire length ofbody 150. According to one aspect of the invention, passage 152 isadapted to retain at least one heating device 158, for example, aninfrared heat source, an inductive heat source, or a convective heatsource, among other devices. Passage 152 may be circular, square,rectangular, or any other shape adapted to retain a heating device 158.According to one aspect, heating device 158 may comprise one or moreheating devices positioned along one or more passages 152. Heatingdevice 158 typically may have a power output of at least about 200watts, typically, at least 500 watts. For instance, heating device 158may be an off-the-shelf infrared light tube. Heating device 158 istypically supplied with electric power by means of a wire or cable andan appropriate electrical connector not shown (for example, through port102 shown in FIG. 7).

Passages 154 and 156 may be coolant or heating fluid flow passages, forexample, passages for transmitting a working fluid, that is, a liquid ora gas, through body 150 to heat or cool body 150 and surface 151. Theworking fluid may be air; nitrogen; water; an inert gas, for example,helium; an oil; or an alcohol, for example, ethylene glycol; among otherworking fluids. Passages 154 and 156 are typically capped at either endby plugs 160. Passages 154 and 156 communicate with two or more workingfluid source conduits 162 and 164 adapted to receive and discharge aworking fluid to and from an external source. Conduits 162 and 164 maybe positioned anywhere along body 150, and, as shown in FIG. 16A, may bepositioned in about the middle of body 150. Conduits 162 and 164 mayhave about ¼-inch nominal diameter and be mounted in conduits 111, asdiscussed below with respect to FIG. 16B. Conduits 162 and 164 typicallysupply working fluid to heat exchanger 86 from a source outside furnace50 (also shown in FIGS. 7-9). For example, coolant flow, such as, air,may be provided to conduit 162 which passes the coolant to passage 156.The coolant may then flow through one or more cross passages (not shown)to passage 154 and then be returned to conduit 164 at a hottertemperature when cooling (or a colder temperature when heating) than thecoolant introduced through conduit 162. The hotter coolant dischargedthrough conduit 164 may be vented or passed through a heat exchanger forcooling (or heating) or to heat recovery, for example, the coolant maybe cooled and reintroduced as coolant to conduit 162. In one aspect, thetemperature of the working fluid introduced to heat exchanger may bevaried to effect the desired temperature of surface 151. For example,the temperature of surface 151 may be regulated by varying thetemperature of the working fluid introduced to heat exchanger 86 bymeans of an external heat exchanger (not shown).

As shown in FIG. 15, heat exchanger 86 is mounted to tube 82 wherebysurface 151 is exposed to the inside of tube 82. Since tube 82 maytypically be made from a material (for example, quartz) having adifferent thermal expansion coefficient than the material (for example,304 stainless steel) of the body 150 of heat exchanger 86, the mountingof heat exchanger 86 to tube may make allowance for differences inthermal expansion. As shown in FIGS. 15-17, in one aspect, heatexchanger 86 may be mounted to tube 82 by means of one or more bracketsor clips 166 and one or more resilient materials 168, for example, oneor more coil springs or flexures. According to this aspect, the clips166 and coil springs 168 provide for a thermally expandable mounting ofheat exchanger 86 to tube 82 while maintaining contact, for example,vapor-tight contact, between surface 151 of body 150 and tube 82.

FIG. 16B is a detailed cross section of the mounting of conduits 162 and164 in conduit 111. Conduit 111 comprises a cylindrical tube, forexample, about ¾-inch nominal diameter, having an open first end 113 anda closed second end 115. Conduits 162 and 164 typically extend fromcylindrical body 150 of heat exchanger 86 and pass through conduit 111and through closed end 115. Conduits 162 and 164 may have an appropriatecoupling 123, for example, the mail pipe coupling shown, to connect to asource of coolant, for example, air. Conduits 162 and 164 may be mountedto the closed end 115 of conduit 111 by means of mechanical fasteners orwelding. Conduits 111 may be mounted to chamber 50, for example, intoports 110 in the rear wall 97 of chamber 50, by means of an appropriatemechanical fastener. For example, port 110 may comprise an appropriatevacuum fitting, for example, an Ultra-Torr® vacuum fitting provided bythe Swagelok Company, or its equivalent fitting. According to aspects ofthe invention, the mounting of conduits 162 and 164 in conduit 111allows for some compliance in the mounting of tubes 82 in furnace 50.For example, the flexibility of the mounting of conduits 162 and 164 inconduit 111 permits some adjustment in the alignment of heat exchanger86 and tube 82 in furnace 50.

As shown in FIG. 17, clip 166 may comprise a thin sheet metal, forexample, stainless steel plate having a thickness of around 0.040inches, bent into a U-shape. The thickness of the plate or sheet fromwhich clip 166 is made may vary from about 0.005 inches to about 0.125inches. Though the aspect of the invention shown in FIGS. 15-17 includesa plurality of clips 166 retaining a plurality of springs 168, aspectsof the invention may include one or more clips 166 or clip-likestructures having the function of clips 166 and one or more spring-likeelements performing the function of springs 168. As shown, the ends 167of clip 166 may be crimped or bent to attach clip 166 to the end of tube82, for example, to a flange of tube 82. Clip 166 may be mounted to body150 by one or more fasteners 170, for example, screws or rivets, throughone or more slotted holes 172 in clip 166. Slotted holes 172 allow clip160 to translate with respect to body 150, for example, due todifferences in thermal expansion. The mounting of heat exchanger 86 totube 82 may also include two or more springs 168, for example, coilsprings or Belleville springs, among others, mounted concentrically oraxially with respect to each other.

FIG. 18A is a right-hand perspective view of a furnace assembly 200according to another aspect of the invention. FIG. 18B is a detailedview of one aspect of the furnace 200 shown in FIG. 18A. FIG. 19 is aleft-hand perspective view of a tube furnace assembly 200 shown in FIG.18A with the extraction assembly extended according to aspects of theinvention. FIG. 20 is a front elevation view of the furnace shown inFIG. 18A. FIG. 21 is a right side elevation view of the furnace shown inFIG. 18A. FIG. 22 is a left side elevation view of the furnace shown inFIG. 18A. FIG. 23 is a cross sectional view of the furnace assembly 200shown in FIGS. 18A-22.

As shown in FIG. 18A, furnace assembly 200 includes a treatment chamber202 and a chamber isolation actuator assembly 204. The contents oftreatment chamber 202 are shown in phantom in FIG. 18A. Treatmentchamber 202 comprises a cylindrical tube 210 capped at a distal end 211by a cover 212. Though shown as a circular cylindrical tube in FIG. 18A,tube 210 may comprise any cylindrical shape, for example, circularcylindrical, rectangular cylindrical, and oval cylindrical, amongothers. Though not shown in FIG. 18A, one or more work pieces, forexample, photovoltaic precursors, may typically be positioned withintube 210, for example, on a support structure or “boat.” The proximalend 213 of tube 210 typically is mounted to a plate 214, for example,for structural support and/or mounting to other fixtures. Treatmentchamber 202 may also include one or more access ports 215, such asflanged ports, for electrical power, instrumentation, or theintroduction or removal (that is, purging or venting) of process fluids.

In a fashion similar to furnace 50 shown in FIGS. 3-9, according toaspects of the invention, work pieces, for example, photovoltaicmaterial precursors, may be treated in treatment chamber 202 withvaporous elements, for example, vaporous Se or S. Furnace assembly 200includes heating means and/or cooling means for treating work piece forexample, according to predetermine temperature schedules, such as theschedule shown in FIG. 2. Furnace assembly 200 may include heating means320 and cooling means 322 in the distal end 211 of tube 210. Heatingmeans 320 may comprise an electric heating element (for example, aconcentric coil heating element) or tubing through which a workingfluid, for example, heated air, water, or oil, may be passed (forexample, a concentric coil tubing). Heating means 320 may be mounted tothe inside or outside surfaces of cover 212 or tube 210 and the heatingmeans may be energized by wire 323. Cooling means 322 may also comprisetubing through which a coolant is passed, for example, one or more ofthe coolants referenced above. The coolant tubing may be provided inconcentric coil or as one or more cooling coils 324 shown in FIGS. 18Aand 23.

As also shown in FIG. 18A, furnace 50 may also include a heatingassembly 400, that is, a heating assembly 400 mounted about cylindricaltube 210. In FIG. 18A, heating assembly 400 is shown in perspectivecross-sectional view. Heating assembly 400 may include a cylindricalhousing 402 having a first end 404 and a second end 406. According toaspects of the invention, cylindrical housing 402 comprises some form ofannular heating elements, for example, infrared, conductive, orconvective heating elements. In one aspect, housing 402 includes atleast one, but typically a plurality of sets of annular heatingelements. In the aspect of the invention shown in FIG. 18A housing 402comprises three sections of heating elements: a first section 401adjacent first end 404 of housing 402; a second middle section 403; andthird section 405 adjacent second end 406 of housing 402. Sections 401,402, and 405 may each include a plurality of heating elements 407, forexample, a plurality of resistive heating elements power and controlledby devices not shown.

First end 404 includes an annular cover plate 408 having an insidediameter 409 sized to accommodate tube 210. Plate 408 that may bemounted to housing 402 by a plurality of mechanical fasteners 410, forexample, screws. Plate 408 may be adapted to thermally isolate theheating assembly 400 from tube 210; for example, plate 408 may be madefrom an insulating material, such as a ceramic. First end 404 may alsoinclude a sealing element 412 adapted to at least partially seal thespace between the outside diameter of tube 210 and inside diameter 409of plate 408. Sealing element 412 may be an elastomeric sealing elementor a fiberglass, such as Nextel fiberglass, or its equivalent. Secondend 404 may include an annular flange 416 having an inside diameter 418.A cover plate 414 may be mounted to annular flange 416 by a plurality ofmechanical fasteners 420, for example, screws. In one aspect, coverplate 414 includes at least one aperture through which cooling means322, heater wire 323, or cooling tube 324 may pass. The apertures incover plate 414 may include a sealing element to minimize the escape offluids.

Heating assembly 400 may include at least one port 422 for introducing acooling medium to and at least one port 424 for removing a coolingmedium from heating assembly 400. Port 422 may comprise a radial hole incylindrical housing 402 for introducing a cooling medium, for example, agas, such as air, or a fluid, such as water, to the cavity 415 betweenheating assembly 400 and tube 210. Port 424 may be adapted to remove themedium introduced. Ports 422 and 424 may be equipped with appropriatefittings (not shown) to facilitate mounting conduits, such as, tubing,to ports 422 and 424.

According to aspects of the invention, heating assembly 400 may beadapted to regulate heating of tube 210 and its contents by means ofindividual heating zones, for example, at least two distinct heatingzones. In the aspect of the invention shown in FIG. 18A, tube 210 isheated by five (5) heating zones. Heating zone 1 may be associated withthe heating means mounted to sealing plate 330, heating zone 2 may beassociated with the heating section 410 in first end 404 of housing 402,heating zone 3 may be associated with the middle heating section 403 ofhousing 402, heating zone 4 may be associated with heating section 405of second end 406 of housing 402, and heating zone 5 may be associatedwith the heating means mounted to cover plate 212. According to aspectsof the invention, the temperature of these zones may be regulated toprovide the desired treatment of the work piece introduced to tube 210,for example, to regulate the heating and/or cooling of a photovoltaicprecursor to provide a solar cell with enhanced performance orreliability.

The isolation of treatment chamber 200 may be effected by chamberisolation actuator assembly 205 that is adapted to compress a sealingplate 330 against an internal flange 332 in cylinder 210 to isolate avolume of cylinder 210. Isolation actuator assembly 205 includes atleast, and typically two, cylinder actuator assemblies 334, a commonmounting plate 335, and a central tube assembly 336. Cylinder actuatorassemblies 334 may each include a long stroke cylinder 338 and a shortstroke cylinder 340. Long stroke cylinder 338 and short stroke cylinder340 may be pneumatic or hydraulic; the fluid control lines are omittedfrom FIGS. 18A and 19. Long stroke cylinders 340 are mounted at a firstend to mounting plate 342 (see FIG. 19), by means of bracket 344 and thesecond end, or working end, of long stroke cylinder 340 is mounted toshort stroke cylinder 340, for example, by means of mechanicalfasteners. Door 342 may represent a portion of a housing into whichfurnace 200 is mounted. Short stroke cylinder 340 is mounted to mountingplate 335 by means of mechanical fasteners. Cylinders 338 and 340displace plate 335 and rod 346 and sealing plate 330. Long strokecylinders 338 may be used for large displacements of sealing plate 330,for example, during gross insertion or extraction. Short strokecylinders 340 may be used for fine displacement of sealing plate 330,for example, during engagement or disengagement of sealing plate 330 andinternal flange 332. FIG. 19 illustrates an aspect of the invention inwhich long stoke cylinders 338 are extended. Mounting plate 335, whichmay be displaced by one or more cylinder actuator assemblies 334, ismounted to support rod or tube 346. Support rod 346 is mounted tosealing plate 330 which is translated with the movement of mountingplate 335. Support rod 346 is positioned inside of central tube assembly336. The displacement of sealing plate 330 may also be practicedmanually, for example, by means of a handle and camming mechanism. Theconfiguration of the sealing plate 330 mounted to a support rod 346,cylinders 338, and ball bearings (not shown) enables a pressure gradientbetween the treatment tube 210 and the area disposed between 214 and theback of the sealing plate 330 to be about one atmosphere.

Central tube assembly 336 provides a housing that, among other things,isolates the inside of tube 210 and supports rod 346. Central tubeassembly 336 includes a flanged nozzle 348 mounted to plate 342, adual-flanged spool 350, a dual flanged bellows assembly 352, and a sealplate 354. Seal 354 may provide a vacuum-tight sealing means between thebellows assembly 352 and mounting plate 335, for example, by means ofone or more elastomeric o-rings 355. According to one aspect of theinvention, seal plate 354 and o-rings 355 are located at a distallocation from the treatment zone in tube 210, that is, between sealingplate 330 and cover plate 212, whereby low-temperature sealing means maybe used and the likelihood of thermal damage to the sealing means isminimized or prevented. This aspect of the invention further comprisesan o-ring disposed between door 342 and plate 214, which allows anadditional low-temperature sealing means. Bellows assembly 352 includesrods 356 which retain the bellows assembly 352 in the compressed statewhen the cylinders 338 retract support rod 346. The compression ofbellows assembly 352 may be varied by means of a biasing device 358, forexample, a spring, a flexure, or a pneumatic cylinder. Central tubeassembly 336 may also include a bearing support for rod 346, forexample, a low-friction bearing or roller bearing (not shown) mountedwithin spool 350, for instance, centrally mounted within spool 350. Thebearing support may support tube 346 during insertion, extraction, andoperation of furnace 200.

As shown most clearly in the detail of FIG. 18B, sealing plate 330 ismounted to support rod 346 by means of short mounting rod 358, forexample, by means of welding or mechanical fastener 360. As shown inFIG. 18B, sealing plate 330 mates with internal annular surface orflange 332 of tube 210 to provide a seal for treatment tube 210. Due tothe high temperatures under which treatment may be practiced, the matingsurfaces of sealing plate 330 and flange 332 typically exhibitmetal-to-metal contact with no additional sealing means there between.In one aspect, a sealing element may be provided, for example, anelasotomeric sealing element that can withstand the typical treatmenttemperatures expected. However, in another aspect of the invention, noelastomeric seals are needed.

In one aspect of the invention, sealing plate 330 may also includeheating or cooling means and provide a surface upon which an element maybe mounted and delivered to tube 210. For example, sealing plate 330 mayinclude an electric heating element or heating fluid coils 362 similarto distal end 211 of tube 210. Also, sealing plate 330 may include tube364 through which a working fluid can be passed. The outer surface oftube 364 may provide a surface (similar to surface 151 of heat exchanger86) to which a treatment element, for example, Se, may be applied andsubsequently volatilized for introducing an element-containing vapor totube 210. An electrical conduit 365 to heat the heating means or thecooling fluid tubing 367 may be located within support tube 346. Forexample, support tube 346 may include tube connections 366 or electricalconnections 368. The tubing or wiring may access the inside of supporttube 346 through an aperture 370 through plate 335 (see FIG. 19).

According to aspects of the invention, tube furnace 200 may be used totreat work pieces, for example, CIG precursors, in a fashion similar tothe operation of furnace 50. Tube furnace 200 may first be “charged”with treatment element, for example, by introducing and heating thesolid element, for example, Se, to volatilize the element, and thencooling to an internal surface of furnace 200 to cause the vaporouselement to condense. In one aspect, the cover plate 212 at the distalend 211 of tube 202 may be cooled by means of cooling tube 324, whichmay extend inside tube 210, whereby the element condenses on an externalsurface of tube 324. As in other aspects of the invention, aftercharging, the work piece to be treated may be introduced to furnace 200,the furnace 200 may be closed by activating isolation actuator assembly205 whereby plate 230 engages flange 232 to isolate tube 210. The workpiece to be treated and the treatment element may then be heated, forexample, according to the schedule shown in FIG. 2, to treat the workpiece and minimize the loss of treatment element.

According to aspects of the present invention, work piece may be treatedin furnaces 50 and 200 by means of the following procedures. Accordingto aspects of the present invention, the temperatures of multipleelements of furnaces 50 and 200 are controlled to optimize thetreatment. For example, as shown in FIG. 18A, the temperature of thesealing plate 330, end plate 212, tube 210 may be independentlycontrolled. With respect to furnace 200, shown in FIG. 3, thetemperature of the tubes 82 and the housing walls (for example, walls 53and 57) may be independently controlled. The following process may bepracticed for both furnace 50 and furnace 200, but the followingdiscussion references furnace 50 only to facilitate the disclosure ofthe invention.

With reference to FIG. 9, furnace 50 is first opened and one or moretreatment elements, for example, Se, is introduced to the furnace. Asnoted above, it is to be understood that the expression “treatmentelement” is used herein to facilitate the disclosure of the invention.The treatment element may comprise a treatment compound comprising twoor more elements. According to aspects of the invention, the elementcomprises elemental sulfur or selenium or combinations of sulfur,selenium, tellurium, indium, gallium, or sodium. The introduction of thetreatment element may be practiced by means of the “charging” processdescribed below. In the following discussion, it is assumed that furnace50 has been charged with Se on the surface 151 of heat exchanger 86shown in FIG. 15.

The work piece to be treated with, for example, Se-containing vapor, isthen introduced to the treatment tubes 82, for example, through opendoor assembly 52 (See FIG. 9.). One or more work pieces may beintroduced to treatment tube 82 on a sheet or tray to facilitatehandling of the work pieces. The work piece introduced to tubes 82 maycomprise any material, but in one aspect, the work piece comprises aphotovoltaic cell precursor deposited on a substrate, such as theprecursor on substrate shown in FIG. 1 6A. The substrate may be ametallic or non-metallic substrate, such as, a glass, a steel, astainless steel, titanium, a ceramic, or a metal-coated plastic, such asa molybdenum-coated polyimide, among other substrate materials. In oneaspect of the invention, where hydrogen may be present during treatment,stainless steel substrates are avoided due to stainless steel'ssusceptibility to hydrogen embrittlement that may cause instability inthe resulting photovoltaic cell. The substrate may be provided as a thinsubstrate having a thickness of between about 5 microns and about 1 mm,for example, as a metallic foil. In the following discussion, referencewill be made to work piece 90, but it will be understood that in aspectsof the invention any material may correspond to work piece 90.

In aspects of the invention, the photovoltaic cell precursor may be anyprecursor material that can be treated with a vaporous element orcompound. In one aspect of the invention, the precursor comprises aprecursor containing one or more elements from group 11 (that is, the“coinage metals”), group 12, group 13, and group 16 (that is, the“chalcogens”) of the Periodic Table (group numbering based upon IUPACconvention; the corresponding groups in the “old” convention being 1B,2B, 3A, and 6A, respectively). For example, in one aspect, the precursormay contain one or more of copper (Cu), indium (In), gallium (Ga),selenium (Se), sulfur (S), or sodium (Na), or combinations thereof. Theprecursor may be a Cu—In—Ga containing material, that is, a “CIG”material; a Cu—In—Ga—Se-containing material; or aCu—In—Ga—Se—S-containing material.

After introducing work piece 90 to be treated into tubes 82, the frontdoor assembly 52 is closed and the furnace 50 is evacuated, for example,by applying a vacuum to one or more of the access ports, for instance avacuum of, typically, about 10⁻³ Torr gage. The furnace 50 may then bepurged with a gas, for example, a dry gas, for instance, a dry inertgas, to remove as much moisture as possible. Heat may so applied toremove moisture. The inert gas may be, for example, nitrogen, argon, orhelium.

According to one aspect of the invention, the treatment tubes 82 may befilled with a treatment gas, for example, a gas that may assist in thesubsequent reaction or treatment. The treatment gas may be a forminggas, such as, hydrogen, nitrogen, or combinations thereof. A treatmentgas that may also be introduced to tubes 82 may include oxygen, hydrogenselenide (H₂Se), hydrogen sulfide (H₂S), or an inert gas, such as argonor helium, among other treatment gases that may be used. For example, asulfur-containing gas, such as H₂S, may be introduced to tubes 82whereby the H₂S is present during the release of Se to effect a S—Setreatment, for example, to produce CIGSS. In one aspect, no forming gasmay be used. The forming gas may also include hydrogen-containing gasother than H₂Se or H₂S, for example, water (H₂O) vapor, ammonia (N₂H₃),an alcohol, or a ketone. In one aspect, the hydrogen-containing gas mayprovide for the in-situ formation of H₂Se during treatment with aSe-containing gas. Trace amounts of hydrogen, for example, in the workpiece or in the chamber, for example, provided by moisture (H₂O) in thechamber, may produce trace amounts of H₂Se formed in situ that, forexample, may react with the work piece. In one aspect of the invention,little or no hydrogen is introduced to the treatment chamber. Forexample, only non-hydrogen-containing gases or no forming gases at allare introduced prior to or during treatment. The gas may be introducedthrough one or more of the ports distributed about furnace 50. A vacuummay also be present in tubes 82. After introducing the gas to furnace50, treatment tubes 82 may be closed, for example, by activating valveactuation assembly 68 whereby sealing assembly 84 engages the openingsof tubes 82, for example, to maintain the gas and/or vacuum within tubes82. After isolation of tubes 82 by sealing assembly 84, the volumebetween the tubes 82 and the walls of furnace 50 may be purged by aninert gas or vacuum to, for example, remove any excess gases ormoisture.

According to aspects of the invention, upon isolation of tubes 82, theheating of the work piece 90 can commence. Again, the heating of workpiece 90 may be practiced according to the heating schedule shown bycurve 32 in FIG. 2 or another similar heating schedule. The heating ofwork piece 90 may be practiced by energizing heating elements 88. Thetemperature of work piece 90 may be monitored by one or more temperaturesensing devices mounted in furnace 50, for example, thermocouples,resistive thermal devices (RTDs), infrared thermocouples, or anon-contact pyrometer. According to aspects of the invention, thetemperature of work piece 90 is elevated to a temperature, for example,above 500 degrees C., at which the vaporous element will react with workpiece 90.

As shown, for example, in FIG. 2, before, at about the same time, orshortly after the heating work piece 90 per curve 32, the temperature ofthe treatment element, for example, the selenium charged to heatexchanger 86, is raised, for example, according to curve 34 in FIG. 2.As discussed above, the temperature of the treatment element may beregulated by controlling the energizing of lamp 158 in heat exchanger 86and/or controlling the flow and/or temperature of working fluid, forexample, air, through heat exchanger 86. For example, the lower the flowof coolant through heat exchanger 86, the hotter the element applied tothe surface of the heat exchanger 86. The temperature of the element israised to a temperature at which the element volatilizes to form anelement-containing vapor, for example, for Se, at least about 100degrees C. However, as discussed above with respect to FIG. 2, forexample, the temperature may be increased to accelerate the release ofelement-containing vapor. For example, Se may be elevated to temperatureof 500 degrees C. or more to release sufficient Se-containing vapor toprovide sufficient reaction with work piece 90. Again, according toaspects of the present invention, the temperature of the treatmentelement may be controlled independently of the control of thetemperature of work piece 90.

After treatment at temperature, the treatment element and the work piece90 may be cooled to complete the treatment, cooled prior to furthertreatment, or cooled for further handling. In one aspect, thetemperature of the element is cooled to encourage the condensation ofthe vaporous element back on the element. This preferred cooling may beeffected by rapidly cooling the element, for example, as shown by curve34 in FIG. 2 and/or maintaining the work piece 90 and other surfacesinside furnace 50 at an elevated temperature, for example, above 170degrees C., to discourage condensation on work piece 90 or on othersurfaces within furnace 50. The element can be cooled by de-energizingor reducing the power on lamp 158 in heat exchanger 86 and/or increasingthe flow of coolant through heat exchanger 86. The cooling of work piece90 may be effected by de-energizing lamps 88. Typically, work piece 90is cooled in a controlled fashion to prevent damage to work piece 90,for example, to prevent cracking or delaminating from the substrate ordamage to the substrate itself. In one aspect, furnace 50 and itscontents, for example, work pieces 90, may be rapidly cooled, forexample, by forced air convective cooling. A cooling fluid my beintroduced to one or more ports of furnace 50, for example, to flangedport 130 and vented through flanged port 140, to rapidly cool furnace 50and its contents. The cooling fluid, for example, air, may be propelledby an air mover, such as a fan or blower, and the fluid may be passedthrough a cooling device, for example, a cooling heat exchanger orchiller.

In one aspect of the invention, the treatment or delivery of work piece90, for example, the selenization of work piece 90, may comprise asteady-state treatment, a pulsed treatment, a cyclic treatment, a rampedtreatment, a dual-source treatment, or a combination thereof. Thetreatment of work piece 90 with the element-containing vapor may bepracticed with an excess amount of element-containing vapor, that is, anamount greater than the stoichiometric amount typically required. Insteady-state treatment, the temperature of work piece 90 and thetreatment element are elevated to treatment temperature, for example,above 400 degrees C., and maintained at the treatment temperature forthe duration of treatment. In pulsed treatment, the temperature of workpiece 90 is maintained at treatment temperature and the temperature ofthe treatment element is varied, for example, varied rapidly duringtreatment. In cyclic treatment, the temperature of work piece 90 ismaintained at treatment temperature and the temperature of the treatmentelement is cyclically varied through, for example, a predeterminedtemperature cycle. In ramped treatment, the temperature of work piece 90is maintained at treatment temperature and the temperature of thetreatment element is ramped, for example, ramped slowly to a desiredtemperature during treatment. In dual source treatment or delivery, agas containing two or more elements, for example, Se and S, may beexposed to work piece 90 at substantially the same time.

Dual treatment may also comprise treatment of work piece 90 with two ormore vaporous elements or compounds provided by two or more heatexchangers (for example, condensers/evaporators). For example, two ormore heat exchanges may be operated at different temperatures dependingupon the volatilization temperature of the element or compound beingdelivered. In one aspect, two or more elements or compounds may bedelivered by one heat exchanger, such as heat exchanger 86 shown in FIG.15, for example, by depositing two or more elements or compounds on thesurface 151 of heat exchanger 86. The two or more elements or compoundsdeposited on the surface of a heat exchanger may typically havedifferent volatilization temperatures, whereby species delivery may bevaried by temperature. In another aspect, two or more elements orcompounds may be delivered by two or more heat exchangers, such as heatexchanger 86 shown in FIG. 15. These two or more heat exchangers adaptedto deliver two or more elements or compounds to a treatment chamber mayinclude isolation devices that limit or prevent the release of one ormore vaporous elements or compounds while one or more of other vaporouselements or compounds are being released to the treatment chamber. Theseisolation devices may comprise seal plate or “flapper valve” typedevices, for example, devices similar to the devices shown in FIGS. 11and 12. The sequence of treatment with the two or more vaporous elementsor compounds may be varied depending upon the desired treatment, forexample, the delivery of the two or more vaporous elements may beprovided individually or substantially simultaneously. Treatment mayalso be practiced repeatedly or alternated from one vaporous element toanother vaporous element. In one aspect, care may be taken to avoid orprevent the condensation of one vaporous element upon another vaporouselement, for example, an element having a higher condensationtemperature. Again, undesirable condensation on treatment elements orcompounds may be avoided by use of suitable isolation means, such as thesealing devices discussed above.

In one aspect of the invention, dual treatment may be practiced forstaged release of treatment vapors. For example, one or more heatexchangers may be used having Se and In and/or Ga compounds deposited ontheir outer surface. The precursor, for example, a Cu—In—Ga precursor,may first be treated with Se by raising the one or more heat exchangersto a first temperature at which Se volatilizes, but In and/or Gacompounds do not. After treatment with Se, the temperature of the one ormore heat exchangers may be raised to volatilize, for example the Incompound. The In compound vapor may then treat the precursor or the Incompound vapor may react with the Se vapor present in the chamber toform indium selenide in situ, where the precursor may then be treatedwith the indium selenide vapor. A similar staged treatment may bepracticed for Ga compounds, where gallium selenide may be formed insitu. Sulfur and In and/or Ga compounds may also be handled in a similarfashion to provide dual treatment with S and In and/or Ga compounds. Inone aspect, this dual treatment may be an effective alternative fortreating copper-rich precursors to provide effective photovoltaicmaterials that could not be formed otherwise. Copper-rich precursors areknown to have inferior performance due to the electrical shorting effectof the excess copper compounds, for example, copper selenide. Dualtreatment of copper-rich precursors according to aspects of theinvention, can improve the performance of the resulting absorber.

The treatment of work piece 90 with the vaporous element may bepracticed repeatedly, for example, three or more times, to provide thedesired treatment. Upon completion of the treatment, sealing assembly 84can be disengaged from treatment tubes 82 and the furnace purged orvented. The vented gases are typically processed to prevent release ofgases to the environment.

FIG. 24 is a schematic block diagram 26 of a process for charging thetreatment element to the enclosure according to one aspect of theinvention. In one aspect of the invention, the “charging” of the elementto the treatment chamber comprises the process of introducing thetreatment element to the treatment enclosure whereby the treatmentelement can be subsequently released in a vaporous form to react withthe work piece being treated. As shown in FIG. 24, the process ofcharging 26 the enclosure with the treatment element may be initiated byintroducing a solid treatment element to an enclosure 40. For example,the treatment element may be introduced as a powder, as beads, or as aningot. The treatment element may be introduced to the enclosure bysimply placing the solid element on the bottom of the enclosure, placinga container (for example, a “boat”) containing the element into theenclosure, or placing the element on an appropriate support means, forexample, a shelf or cavity, located in the enclosure. The element mayalso be automatically fed into the furnace, for example, by means of anautomated feeder, for example, an automated wire-element feeder. Asnoted above, it is to be understood that the expression “treatmentelement” is used herein to facilitate the disclosure of the invention.The treatment element may comprise a treatment compound comprising twoor more elements. According to aspects of the invention, the solidelement or compound introduced to the treatment chamber may be anelement of group 11, 12, 13, or 16 of the Periodic Table, for example,selenium, sulfur, indium, gallium, indium selenide, indium sulfide,gallium selenide, gallium sulfide, or combinations thereof. The elementor compound may also include sodium or a sodium-containing compound.

Next, the enclosure is closed, sealed, or otherwise isolated 41 tominimize or prevent the leakage of vaporous element from the enclosure.In one aspect, after isolating the enclosure 41, the enclosure may beevacuated, for example, by applying a vacuum to the enclosure. In oneaspect, a typical vacuum of 10⁻³ Torr gage may be applied to theenclosure. The vacuum may be maintained during the charging process.When the enclosure includes an internal treatment chamber, for example,the tube 82 shown in FIG. 16A, process 26 may include the optional step47 of isolating the internal treatment chamber. This isolation of theinternal chamber may be practiced using a chamber isolation assembly,such as sealing assembly 84 shown in FIGS. 11 and 12, for example, wherea “flapper” valve isolates the internal chamber.

As shown in FIG. 24, according to process 26, the treating element isthen heated 42 to a temperature above which the element will volatilizeat the prevailing pressure; for example, when the treatment element isSe, the Se is heated to a temperature of between about 100 and about 400degrees C. The heating of step 42 may, for example, be effected byinfrared lamps 88 shown in FIG. 10, heating assembly 400 shown in FIG.18A, or heating coils 320 shown in FIG. 18A. At this temperature, the Sebegins to volatilize to create a selenium-containing gas into theenclosure. However, to increase the volatilization, the temperature ofthe element may typically be increased to a temperature greater than theinitial volatilization temperature to ensure a plentiful supply of thevaporous element. For example, when Se is used, the Se is typicallyheated to at least about 500 degrees C. to ensure an adequate supply ofSe in vaporous form.

Prior to, during, or after the heating the treatment element 42, atleast one surface inside the enclosure is cooled 43 to provide atemperature less than the temperature at which the element volatilizes.For example, again, for Se, this temperature may typically be atemperature less than 100 degrees C., for example, a temperature ofabout 80 degrees C. or lower. In one aspect, the cooling is practiced tomaintain the surface at a temperature below the vapor pressuretemperature of the element, for example, Se or S. The cooling of asurface inside the enclosure is typically provided by some form of heatexchanger having a working fluid passing through it. One typical heatexchanger that may be used for aspects of this invention is heatexchanger 86 shown in and described with respect to FIGS. 15-17.According to aspects of the invention shown in FIG. 24, the cooledsurface of the heat exchanger provides a condensation site for thecondensation 44 of the vaporous element provided by heating 42. Theheating 42, cooling 43, and condensing 44 steps of the charging process26 may be practiced repeatedly (for example, three or more times) or foran extended period of time (for example, at least about 20 minutes) toprovide the desired content of treatment element on a surface inside theenclosure.

After sufficient element has been condensed upon the surface, thesurface and solid element may be cooled 45 (assuming that the solidelement has not completely volatilized) to terminate the volatilization.In one aspect, the cooling of the surface and the treatment element ispracticed rapidly, for example, at rate of at least about 10° C./min, toallow at least some of the vaporous element released in step 42 tocondense onto the solid element and/or surface. This recapture of thetreatment element through controlled or rapid cooling of the solidelement and/or surface minimizes the loss of the element to condensationon other surfaces of the enclosure and related structures. In oneaspect, during cooling of the element for recapture, the temperature ofthe surfaces of the enclosure and of any surfaces within the enclosuremay be maintained at an elevated temperature, for example, a temperatureabove 170 degrees C. for Se, to discourage condensation on surfacesother than the cooled surface or solid element. When cooling of theelement 45 is completed, the element may be removed from the enclosure46. When an internal chamber is used, process 26 may also include thestep of opening the internal chamber, for example, disengaging thesealing assembly 84 shown in FIGS. 11 and 12. The enclosure, and anyinternal treatment chambers, may be vented, for example, in preparationfor subsequent treatment in the enclosure. With completion of thecharging process 26, with treatment element provided on a surface withinthe enclosure, the treatment of a work piece as shown and described withrespect to FIGS. 1 and 2 may commence.

FIG. 25 is a plot 300 of treatment element vapor pressure as a functionof temperature for selenium, though a similar curve may be provided forother treatment elements. FIG. 26 is a plot 310 of heat exchanger (forexample, condenser/evaporator) temperature as a function of coolant flowaccording to one aspect of the invention. The curves shown in FIG. 26were determined for one specific heat exchanger, for example, the tubetype device shown in FIGS. 18A through 23. Similar curves may beprovided for other heat exchangers relating coolant flow to temperature.The curves for other heat exchangers may vary depending upon the size ofthe heat exchanger, the type of coolant used, and the thermalcharacteristics of the material from which the heat exchanger is made,among other things. According to one aspect of the invention, the curvesshown in FIGS. 25 and 26 may be used in conjunction with the curvesshown in FIG. 2 to control the operation of a treatment furnace, forexample, to control the operation of furnace 50 shown in FIGS. 3-9 orfurnace 200 shown in FIGS. 18-23.

As shown in FIG. 25, the curve 302 in plot 300 represents therelationship of the vapor pressure of selenium, in Torr, as shown in thelog scale on ordinate 304 in FIG. 26, and temperature, in degrees C,shown on abscissa 303. Clearly, the vapor pressure of selenium increaseswith temperature. Plot 310 in FIG. 26 displays three curves 312, 314,and 316 that correspond to the relationship of the heat exchangertemperature (for example, evaporator/condenser), in degrees C, as shownon ordinate 318 for three furnace temperatures as a function of coolantflow, in standard cubic feet per minute (SCFM), shown on the abscissa320. In the aspect of the invention shown in FIG. 26, curves 312, 314,and 315 correspond to representative furnace temperatures of 300 degreesC., 400 degrees C., and 500 degrees C., respectively. Again, the shapeand magnitude of curves 312, 314, and 318 may vary for other heatexchangers or other furnace operating temperatures.

According to aspects of the present invention, the curves that appear inFIGS. 2, 25, and 26 may be used to control the operation of a treatmentfurnace as follows. FIG. 2 provides one desired temperature schedule fortreating a work piece, for example, a photovoltaic precursor, with avaporous element, for example, vaporous selenium or sulfur. As discussedabove, to ensure an adequate supply of vaporous element, for example,Se, to obtain the desired reaction with the work piece, for example, theprecursor, the temperature of the element is increased to provide adesired partial pressure of element vapor in the treatment chamber. Thedesired partial pressure for one aspect of the invention is shown bycurve 35 in FIG. 2. In order to obtain this element partial pressure,the temperature of the element must be regulated according to thetemperature-pressure curve 302 shown in FIG. 25. The temperaturedetermined by curve 302 is then used to regulate the flow of coolantthrough the heat exchanger as indicated by curves 312, 314, and 316 inFIG. 26. The flow of coolant, for example, air, to the heat exchanger isthen regulated, for example, by a control valve, to obtain the desiredcoolant flow. In another aspect of the invention, the temperature of thecoolant, for example, air, may be varied to effect the desired elementtemperature. For example, the temperature of the coolant may beregulated by varying the temperature of a heat exchanger adapted to heator cool the working fluid, for example, an external heat exchangerhaving a working fluid passing through it.

For example, assuming that from curve 35 in FIG. 2, the desired partialpressure for treating a precursor with Se at a temperature T_(E3) isabout 1.0 Torr. From FIG. 25, curve 302, and pressure 1.0 Torr onordinate 304, the desired heat exchanger temperature is about 350degrees C. By comparing a desired heat exchanger temperature of 350degrees C. with curve 316 in FIG. 26, a desired heat exchanger flow rateof, for example, about 14 standard cubic feet per hour (SCFH) isobtained. Therefore, to obtain the desired temperature T_(E3), the flowof coolant, for example, air, through the heat exchanger is regulated toabout 14 SCFH. The flow of coolant, for example, air, through a heatexchanger according to aspects of the invention may vary from about 10SCFH to about 25 SCFM, and is typically between about 0.1 SCFM and 3SCFM.

This control of the operation of the coolant flow to regulate the heatexchanger may be practiced manually, but is preferably, practiced in anautomated fashion, for example, by means of computer, programmable logiccontroller (PLC), temperature feedback loop, PID controller, or anotherautomated controller. For example, in one aspect, the curves illustratedin FIGS. 2, 25, and 26, may be programmed into a computer or PLC andoperated to control the operation of, for example, an automated valvecontroller of a coolant flow valve.

The methods and apparatus according to aspects of the inventiondescribed above may be used to manufacture an improved photovoltaicmaterial, for example, a material having little or no hydrogen content.Such a material has the advantage of not being prone to thedeterioration in performance that characterizes prior art materialshaving hydrogen. For example, as discussed above, in one aspect of theinvention, a precursor may be treated with a treatment gas, such as aselenium-containing vapor, with little or no presence of hydrogen. Inprior art methods, selenium is typically introduced in the form of H₂Sewhereby hydrogen (H) inherently is introduced to the reaction and to theabsorber matrix. According to aspects of the invention, the treatmentchamber can be effectively purged of essentially all hydrogen by meansof vacuum and/or non-hydrogen purge gas. As a result, the precursor, forexample, the CIG precursor, can be treated with a Se— or S-containingvapor (that is, a H-free vapor) to produce an essentially H-freeabsorber. In one aspect of the invention, the absorber comprises a CIGSabsorber having less then 5% hydrogen content, or typically less than 1%hydrogen content, or can be substantially hydrogen free. Such alow-hydrogen or hydrogen free absorber, for example, a low-H or H-freeCIGS or CIGSS absorber, can provide more reliable performance withoutthe degradation that characterizes hydrogen-containing absorbers.

The control and operation of furnaces 50 and 200 may be performedmanually or by means of one or more automated controllers, for example,a personal computer or PLC. These control devices may include speciallydesigned software designed to monitor and control the operation offurnaces 50 and 200. Furnaces 50 and 200 may typically include sensors,for example, temperature sensors, pressure sensors, and flow sensors,and controllers, for example, automatic temperature, pressure, or flowcontrollers to regulate and control the operation of furnaces 50 and200. The electrical connections associated with these sensors andcontrollers may pass through one or more of the many access portsassociated with furnaces 50 and 200.

In one aspect of the invention, the methods and apparatuses disclosedherein may be practiced or utilized in a batch mode, for example, one ormore work pieces may be treated in furnaces 50 or 200 and the workpieces removed for subsequent treatment of further work pieces. However,according to another aspect of the invention, the methods andapparatuses disclosed herein may be adapted for continuous treatmentwhereby a substantially continuous flow of work pieces may be processedaccording to the disclosed methods or handled by, for example,introduced and removed from, the disclosed apparatus. In one aspect,unlike the temperature variations shown FIG. 2, the treatment conditionsof the continuous methods may be substantially stable as work pieces areintroduced and removed from the treatment chambers.

Aspects of the present invention provide improved means of treating workpieces, especially, improved means of treating and producingphotovoltaic cells. Methods and apparatus according to aspects of thepresent invention can assist in reducing the production costs ofphotovoltaic cells whereby photovoltaic energy can be a cost effectivealternative to the diminishing supply of fossil fuels.

While several aspects of the present invention have been described anddepicted herein, alternative aspects may be conceived by those skilledin the art to accomplish the same objectives. Accordingly, it isintended by the appended claims to cover all such alternative aspectsthat fall within the true spirit and scope of the invention.

1-63. (canceled)
 64. A photovoltaic cell comprising: a substrate; and an absorber deposited on to the substrate, the absorber comprising elements from each of group 11, group 12, and group 13 of the Periodic Table, and less than 5% hydrogen.
 65. The photovoltaic cell as recited in claim 64, wherein the absorber comprises less than 1% hydrogen.
 66. The photovoltaic cell as recited in claim 65, wherein the absorber comprises substantially no hydrogen.
 67. The photovoltaic cell as recited in claim 64, wherein the absorber further comprises at least one of selenium and sulfur.
 68. The photovoltaic cell as recited in claim 64, wherein the substrate comprises a metallic substrate.
 69. The photovoltaic cell as recited in claim 64, wherein the substrate comprises at least one of steel, stainless steel, titanium, and glass.
 70. The photovoltaic cell as recited in claim 64, wherein the cell further comprises an electrical conductor mounted to the absorber. 71-74. (canceled)
 75. The photovoltaic cell as recited in claim 64, wherein the absorber comprises copper, indium, and gallium.
 76. The photovoltaic cell as recited in claim 64, wherein the substrate comprises a metallic foil.
 77. The photovoltaic cell as recited in claim 76, wherein the metallic foil has a thickness between about 5 microns and about 1 mm.
 78. The photovoltaic cell as recited in claim 64, wherein the photovoltaic cell is more reliable than a photovoltaic cell containing more than about 5% hydrogen.
 79. A method of fabricating a low-hydrogen containing photovoltaic cell from the substrate and absorber recited in claim 1, the method comprising: introducing the substrate and the absorber to an enclosure; introducing an element-containing material having little or no hydrogen content to the enclosure; heating the substrate and the absorber to a first temperature; independent of the heating of the substrate and the absorber, heating the element-containing material to a temperature sufficient to volatilize the element and release an element-containing vapor into the enclosure; treating the absorber with at least some of the element-containing vapor; and cooling the substrate and the absorber to provide a low-hydrogen containing photovoltaic cell.
 80. The method as recited in claim 79, wherein the method further comprises introducing a substantially hydrogen-free treatment gas to the enclosure to provide a substantially hydrogen-free reaction atmosphere.
 81. The method as recited in claim 80, wherein the substantially hydrogen-free gas comprises at least one of oxygen, argon, helium, selenium vapor and sulfur vapor.
 82. The method as recited in claim 79, wherein the method further comprises vacuum purging the enclosure.
 83. The method as recited in claim 79, wherein the method further comprises, after reacting, regulating the temperature of the element-containing material at a temperature sufficient to condense at least some of the element from the element-containing vapor on the element-containing material.
 84. The method as recited in claim 79, wherein the element-containing material comprises one of sulfur, selenium, tellurium, indium, gallium, sodium, and combinations thereof.
 85. The method as recited in claim 79, wherein treating the absorber with at least some of the element-containing vapor comprises one of reacting the element-containing vapor with the absorber and providing an overpressure of the element-containing vapor to the absorber.
 86. The method as recited in claim 79, wherein cooling the element-containing material comprises cooling the element-containing material wherein substantially all of the unreacted element-containing vapor condenses on the element-containing material.
 87. The method as recited in claim 79, wherein the method further comprises mounting an electrical conductor to the absorber. 